feat: Add user attribution to Linear integration with actor authorization (#11774)

- Add `actor=app` parameter to Linear OAuth authorization URL for
consistent app-level authorization
https://linear.app/developers/oauth-actor-authorization
- Implement user attribution for Linear issue creation and linking using
`createAsUser` and `displayIconUrl` parameters
- Enhance Linear integration to properly attribute actions to specific
Chatwoot agents

**Note**
- The displayIconUrl parameter is being sent correctly to Linear's
GraphQL API (verified through testing), but there is an issues with icon
is not attaching properly.
- We might need to disconnect the integration connect again.

lib/linear/mutations.rb

@@ -32,10 +32,22 @@ module Linear::Mutations
     GRAPHQL
   end
 
-  def self.issue_link(issue_id, link, title)
+  def self.issue_link(params)
+    issue_id = params[:issue_id]
+    link = params[:link]
+    title = params[:title]
+    user_name = params[:user_name]
+    user_avatar_url = params[:user_avatar_url]
+
+    user_params = []
+    user_params << "createAsUser: #{graphql_value(user_name)}" if user_name.present?
+    user_params << "displayIconUrl: #{graphql_value(user_avatar_url)}" if user_avatar_url.present?
+
+    user_params_str = user_params.any? ? ", #{user_params.join(', ')}" : ''
+
     <<~GRAPHQL
       mutation {
-        attachmentLinkURL(url: "#{link}", issueId: "#{issue_id}", title: "#{title}") {
+        attachmentLinkURL(url: "#{link}", issueId: "#{issue_id}", title: "#{title}"#{user_params_str}) {
           success
           attachment {
             id