feat(mattermost): add auth and send message to channel action

* feat: mattermost integration

* post review adjustments

packages/docs/pages/.vitepress/config.js

@@ -142,6 +142,15 @@ export default defineConfig({
             { text: 'Connection', link: '/apps/http-request/connection' },
           ],
         },
+        {
+          text: 'Mattermost',
+          collapsible: true,
+          collapsed: true,
+          items: [
+            { text: 'Triggers', link: '/apps/mattermost/actions' },
+            { text: 'Connection', link: '/apps/notion/connection' },
+          ],
+        },
         {
           text: 'Notion',
           collapsible: true,

packages/docs/pages/apps/mattermost/actions.md

@@ -0,0 +1,12 @@
+---
+favicon: /favicons/mattermost.svg
+items:
+  - name: Send a message to channel
+    desc: Sends a message to a channel you specify.
+---
+
+<script setup>
+  import CustomListing from '../../components/CustomListing.vue'
+</script>
+
+<CustomListing />

packages/docs/pages/apps/mattermost/connection.md

@@ -0,0 +1,19 @@
+# Mattermost
+
+:::info
+This page explains the steps you need to follow to set up the Mattermost
+connection in Automatisch. If any of the steps are outdated, please let us know!
+:::
+
+1. Go to the `<WORKSPACE_NAME>/integrations/oauth2-apps/add` page of your Mattermost server to register a **new OAuth application**.
+   - You can find details about registering new Mattermost oAuth application at https://docs.mattermost.com/integrations/cloud-oauth-2-0-applications.html#register-your-application-in-mattermost.
+2. Fill in the **Display Name** field.
+3. Fill in the **Description** field.
+4. Fill in the **Homepage** field.
+5. Copy **OAuth Redirect URL** from Automatisch to the **Callback URLs** field on Mattermost page.
+6. Click on the **Save** button at the end of the form on Mattermost page.
+7. Copy the **Client ID** value from the following page to the `Client ID` field on Automatisch.
+8. Copy the **Client Secret** value from the same page to the `Client Secret` field on Automatisch.
+9. Click **Done** button on MAttermost page.
+10. Click **Submit** button on Automatisch.
+11. Congrats! Start using your new Mattermost connection within the flows.

packages/docs/pages/guide/available-apps.md

@@ -18,6 +18,7 @@ Following integrations are currently supported by Automatisch.
 - [Google Forms](/apps/google-forms/triggers)
 - [Google Sheets](/apps/google-sheets/triggers)
 - [HTTP Request](/apps/http-request/actions)
+- [Mattermost](/apps/mattermost/actions)
 - [Notion](/apps/notion/triggers)
 - [Ntfy](/apps/ntfy/actions)
 - [Odoo](/apps/odoo/actions)