feat: New APIs for search (#6564)

- Adding new API endpoints for search
- Migrations to add appropriate indexes

app/views/api/v1/accounts/search/index.json.jbuilder

@@ -0,0 +1,32 @@
+json.payload do
+  json.conversations do
+    json.array! @result[:conversations] do |conversation|
+      json.id conversation.display_id
+      json.account_id conversation.account_id
+      json.created_at conversation.created_at.to_i
+      json.message do
+        json.partial! 'message', formats: [:json], message: conversation.messages.try(:first)
+      end
+      json.contact do
+        json.partial! 'contact', formats: [:json], contact: conversation.contact if conversation.try(:contact).present?
+      end
+      json.inbox do
+        json.partial! 'inbox', formats: [:json], inbox: conversation.inbox if conversation.try(:inbox).present?
+      end
+      json.agent do
+        json.partial! 'agent', formats: [:json], agent: conversation.assignee if conversation.try(:assignee).present?
+      end
+    end
+  end
+  json.contacts do
+    json.array! @result[:contacts] do |contact|
+      json.partial! 'contact', formats: [:json], contact: contact
+    end
+  end
+
+  json.messages do
+    json.array! @result[:messages] do |message|
+      json.partial! 'message', formats: [:json], message: message
+    end
+  end
+end