feat: Separate indexing with the search feature (#12503)

With this change, the indexing would be separate from the search, so you
need to enable indexing on the cloud and run it. It should start
indexing the messages to ElasticSearch/OpenSearch. Once indexing is
completed, we can turn on the feature for the customer.


Make sure that the following is done when you deploy.
Set POSTGRES_STATEMENT_TIMEOUT=600s before you run the indexing.

1. Make sure that the account with advanced_search has
advanced_search_indexing enabled
```rb
Account.feature_advanced_search.each do |account|
  account.enable_features(:advanced_search_indexing)
  account.save!
end
```

2. Enable indexing for all accounts with paid subscription.
```rb
Account.where("custom_attributes ->> 'plan_name' IN (?)", ['Enterprise', 'Startups', 'Business']).each do |account|
account.enable_features(:advanced_search_indexing)
  account.save!
end
```

3. Run indexing for all the messages.
```rb
Message.reindex
```

Co-authored-by: Vishnu Narayanan <iamwishnu@gmail.com>
Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

config/features.yml

@@ -209,3 +209,8 @@
   display_name: SAML
   enabled: false
   premium: true
+- name: advanced_search_indexing
+  display_name: Advanced Search Indexing
+  enabled: false
+  premium: true
+  chatwoot_internal: true