feat: Linear OAuth 2.0 (#10851)

Fixes https://linear.app/chatwoot/issue/CW-3417/oauth-20-authentication
We are planning to publish the Chatwoot app in the Linear [integration
list](https://linear.app/docs/integration-directory). While we currently
use token-based authentication, Linear recommends OAuth2 authentication.
This PR implements OAuth2 support.

---------

Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

app/controllers/api/v1/accounts/integrations/linear_controller.rb

@@ -1,5 +1,11 @@
 class Api::V1::Accounts::Integrations::LinearController < Api::V1::Accounts::BaseController
   before_action :fetch_conversation, only: [:link_issue, :linked_issues]
+  before_action :fetch_hook, only: [:destroy]
+
+  def destroy
+    @hook.destroy!
+    head :ok
+  end
 
   def teams
     teams = linear_processor_service.teams
@@ -90,4 +96,8 @@ class Api::V1::Accounts::Integrations::LinearController < Api::V1::Accounts::Bas
   def permitted_params
     params.permit(:team_id, :project_id, :conversation_id, :issue_id, :link_id, :title, :description, :assignee_id, :priority, label_ids: [])
   end
+
+  def fetch_hook
+    @hook = Integrations::Hook.where(account: Current.account).find_by(app_id: 'linear')
+  end
 end