Add a column zoekt_settings in application_settings

What does this MR do and why?

Add a new column zoekt_settings of the type jsonb in the application_settings table. This jsonb column can have three attributes.

• zoekt_indexing_enabled
• zoekt_indexing_paused
• zoekt_search_enabled

This column can be used to show the settings in the admin panel and eventually, few zoekt feature flags can be deprecated.

All three attributes have the default value of false. In the follow-up MRs the backfilling of this column will happen.

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Before	After

How to set up and validate locally

• Check out the branch and run the DB migrations.

git fetch && git checkout 389765-add-zoekt_settings-in-application_settings && bin/rails db:migrate

• Open the rails console

bin/rails c

• Check the existing ApplicationSetting record. The value of zoekt_settings should be {}

ApplicationSetting.last.zoekt_settings

• Check the new ApplicationSetting record. The value of zoekt_settings should be {"zoekt_indexing_enabled"=>false, "zoekt_indexing_paused"=>false, "zoekt_search_enabled"=>false}

ApplicationSetting.new.zoekt_settings

Related to #389765

#452041 (closed)