[client] disambiguate the connection_type metric tag (#7043)

## Describe your changes

`recordConnectionMetrics` mapped only `conntype.Relay` to `relay` and
let a `default` branch
record everything else as `ice`. That silently included `ICETurn` — an
ICE connection through
a TURN server, which
[`conn.isRelayed`](https://github.com/netbirdio/netbird/blob/main/client/internal/peer/conn.go#L788-L795)
itself counts as relayed — and `None`, the transient state set when the
relay drops

([conn.go:632](https://github.com/netbirdio/netbird/blob/main/client/internal/peer/conn.go#L632))
or the peer state is reset
([conn.go:757](https://github.com/netbirdio/netbird/blob/main/client/internal/peer/conn.go#L757)).
Both were reported as direct peer-to-peer, so the `ice` share overstated
direct connections on
every platform.

The mapping now lists every priority explicitly and emits `ice_p2p`,
`ice_turn`, `relay` or
`unknown`. The new values deliberately do not reuse `ice` to avoid
ambuguity.


## Issue ticket number and link

No public issue. Found while reviewing the first production sample of
client metrics: 38% of iOS
connection events were tagged `ice` on a platform that forces relay by
default, which traced back
to the `default` branch at
[client/internal/peer/conn.go#L963-L968](https://github.com/netbirdio/netbird/blob/main/client/internal/peer/conn.go#L963-L968).

## Stack

<!-- branch-stack -->

### Checklist
- [x] Is it a bug fix
- [ ] Is a typo/documentation fix
- [ ] Is a feature enhancement
- [ ] It is a refactor
- [x] Created tests that fail without the change (if possible)

> By submitting this pull request, you confirm that you have read and
agree to the terms of the [Contributor License
Agreement](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTOR_LICENSE_AGREEMENT.md).

## Documentation
Select exactly one:

- [] I added/updated documentation for this change
- [x] Documentation is **not needed** for this change (explain why)

Internal metrics documentation only, in
`client/internal/metrics/infra/README.md`: the four
`connection_type` values with their derivation, and a note that pre-fix
`ice` samples are not
comparable with `ice_p2p`. No public API, CLI or configuration change,
so no netbirdio/docs PR.

### Docs PR URL (required if "docs added" is checked)
Paste the PR link from https://github.com/netbirdio/docs here:

N/A

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

## Summary by CodeRabbit

* **New Features**
* Connection metrics now distinguish direct peer-to-peer, TURN-assisted,
relay, and unknown connection types.
  * Metrics include clearer connection and peer identification details.

* **Documentation**
* Updated connection timing metric values, traffic semantics, priority
behavior, and historical data guidance.

* **Bug Fixes**
* Unset or unrecognized connection priorities are no longer incorrectly
classified as peer-to-peer.
* Unknown-transport metrics are skipped to prevent misleading connection
data.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

client/internal/peer/conn.go

@@ -961,12 +961,9 @@ func (conn *Conn) recordConnectionMetrics() {
 	priority := conn.currentConnPriority
 	conn.mu.Unlock()
 
-	var connType metrics.ConnectionType
-	switch priority {
-	case conntype.Relay:
-		connType = metrics.ConnectionTypeRelay
-	default:
-		connType = metrics.ConnectionTypeICE
+	connType := metricsConnType(priority)
+	if connType == metrics.ConnectionTypeUnknown {
+		return
 	}
 
 	// Record metrics with timestamps - duration calculation happens in metrics package
@@ -1067,3 +1064,16 @@ func boolToConnStatus(connected bool) guard.ConnStatus {
 	}
 	return guard.ConnStatusDisconnected
 }
+
+func metricsConnType(priority conntype.ConnPriority) metrics.ConnectionType {
+	switch priority {
+	case conntype.Relay:
+		return metrics.ConnectionTypeRelay
+	case conntype.ICETurn:
+		return metrics.ConnectionTypeICETurn
+	case conntype.ICEP2P:
+		return metrics.ConnectionTypeICEP2P
+	default:
+		return metrics.ConnectionTypeUnknown
+	}
+}

client/internal/peer/conn_test.go

@@ -11,6 +11,8 @@ import (
 	"github.com/stretchr/testify/assert"
 
 	"github.com/netbirdio/netbird/client/iface"
+	"github.com/netbirdio/netbird/client/internal/metrics"
+	"github.com/netbirdio/netbird/client/internal/peer/conntype"
 	"github.com/netbirdio/netbird/client/internal/peer/dispatcher"
 	"github.com/netbirdio/netbird/client/internal/peer/guard"
 	"github.com/netbirdio/netbird/client/internal/peer/ice"
@@ -386,3 +388,33 @@ func TestConn_onWGDisconnected_NoEscalationWithoutRosenpass(t *testing.T) {
 	}
 	assert.Empty(t, disconnected, "escalation must be limited to rosenpass connections")
 }
+
+func TestMetricsConnType(t *testing.T) {
+	tests := []struct {
+		name     string
+		priority conntype.ConnPriority
+		expected metrics.ConnectionType
+	}{
+		{"relay", conntype.Relay, metrics.ConnectionTypeRelay},
+		{"ice over turn is relayed, not p2p", conntype.ICETurn, metrics.ConnectionTypeICETurn},
+		{"direct p2p", conntype.ICEP2P, metrics.ConnectionTypeICEP2P},
+		{"unset priority is unknown, not p2p", conntype.None, metrics.ConnectionTypeUnknown},
+		{"unrecognised priority is unknown", conntype.ConnPriority(99), metrics.ConnectionTypeUnknown},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			assert.Equal(t, tc.expected, metricsConnType(tc.priority))
+		})
+	}
+}
+
+func TestMetricsConnType_RelayedMatchesIsRelayed(t *testing.T) {
+	for _, priority := range []conntype.ConnPriority{conntype.None, conntype.Relay, conntype.ICETurn, conntype.ICEP2P} {
+		conn := &Conn{currentConnPriority: priority}
+		tag := metricsConnType(priority)
+		relayedTag := tag == metrics.ConnectionTypeRelay || tag == metrics.ConnectionTypeICETurn
+		assert.Equal(t, conn.isRelayed(), relayedTag,
+			"priority %s: isRelayed and the %q metric tag must agree", priority, tag)
+	}
+}