[4543] & [4529] - Add a channel avatar handler to MessageListHeader and update docs

[MarinTolic]

🎯 Goal

closes #4543
closes #4529

🛠 Implementation details

• Added a new handler to MessageListHeader
• Updated the docs

🧪 Testing

Patch that implements the new handler

Index: stream-chat-android-compose-sample/src/main/java/io/getstream/chat/android/compose/sample/ui/MessagesActivity.kt
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/stream-chat-android-compose-sample/src/main/java/io/getstream/chat/android/compose/sample/ui/MessagesActivity.kt b/stream-chat-android-compose-sample/src/main/java/io/getstream/chat/android/compose/sample/ui/MessagesActivity.kt
--- a/stream-chat-android-compose-sample/src/main/java/io/getstream/chat/android/compose/sample/ui/MessagesActivity.kt	(revision f1d060ce85b7afc688375ea0e385d66a80d784ca)
+++ b/stream-chat-android-compose-sample/src/main/java/io/getstream/chat/android/compose/sample/ui/MessagesActivity.kt	(date 1669738446388)
@@ -19,6 +19,7 @@
 import android.content.Context
 import android.content.Intent
 import android.os.Bundle
+import android.widget.Toast
 import androidx.activity.compose.setContent
 import androidx.activity.viewModels
 import androidx.compose.foundation.ExperimentalFoundationApi
@@ -98,7 +99,10 @@
                     onBackPressed = {
                         finish()
                     },
-                    onHeaderActionClick = {}
+                    onHeaderActionClick = {},
+                    onChannelAvatarClick = {
+                        Toast.makeText(applicationContext,"hi",Toast.LENGTH_SHORT).show()
+                    }
                 )
 
                 // MyCustomUi()

1. Apply the patch above
2. Enter a channel
3. Click on the channel avatar in the messages screen

Expected: Should show toast

☑️Contributor Checklist

General

• Assigned a person / code owner group (required)
• Thread with the PR link started in a respective Slack channel (#android-chat-core or #android-chat-ui) (required)
• PR targets the develop branch
• PR is linked to the GitHub issue it resolves

Code & documentation

• Changelog is updated with client-facing changes
• New code is covered by unit tests
• Comparison screenshots added for visual changes
• Affected documentation updated (KDocs, docusaurus, tutorial)

☑️Reviewer Checklist

• UI Components sample runs & works
• Compose sample runs & works
• UI Changes correct (before & after images)
• Bugs validated (bugfixes)
• New feature tested and works
• Release notes and docs clearly describe changes
• All code we touched has new or updated KDocs

🎉 GIF

[skydoves]

Overall looks good to me!

[filbabic]

☑️Reviewer Checklist

• UI Components sample runs & works
• Compose sample runs & works
• UI Changes correct (before & after images)
• Bugs validated (bugfixes)
• New feature tested and works
• Release notes and docs clearly describe changes
• All code we touched has new or updated KDocs