[misc] Move shared components to shared directory (#4286)

Moved the following directories:

```
  - management/client → shared/management/client
  - management/domain → shared/management/domain
  - management/proto → shared/management/proto
  - signal/client → shared/signal/client
  - signal/proto → shared/signal/proto
  - relay/client → shared/relay/client
  - relay/auth → shared/relay/auth
```

and adjusted import paths

shared/management/client/rest/options.go

@@ -0,0 +1,44 @@
+package rest
+
+import "net/http"
+
+// option modifier for creation of Client
+type option func(*Client)
+
+// HTTPClient interface for HTTP client
+type HttpClient interface {
+	Do(req *http.Request) (*http.Response, error)
+}
+
+// WithHTTPClient overrides HTTPClient used
+func WithHttpClient(client HttpClient) option {
+	return func(c *Client) {
+		c.httpClient = client
+	}
+}
+
+// WithBearerToken uses provided bearer token acquired from SSO for authentication
+func WithBearerToken(token string) option {
+	return WithAuthHeader("Bearer " + token)
+}
+
+// WithPAT uses provided Personal Access Token
+// (created from NetBird Management Dashboard) for authentication
+func WithPAT(token string) option {
+	return WithAuthHeader("Token " + token)
+}
+
+// WithManagementURL overrides target NetBird Management server
+func WithManagementURL(url string) option {
+	return func(c *Client) {
+		c.managementURL = url
+	}
+}
+
+// WithAuthHeader overrides auth header completely, this should generally not be used
+// and WithBearerToken or WithPAT should be used instead
+func WithAuthHeader(value string) option {
+	return func(c *Client) {
+		c.authHeader = value
+	}
+}