Make advanced search indexing timeout configurable

Proposal

Right now the project indexing timeout is hardcoded in indexer.rb to 30 minutes.

      include Gitlab::Loggable

      TIMEOUT = 30.minutes.to_i
      Error = Class.new(StandardError)
      BLOB_SCHEMA_VERSION = 23_08

If a project is large or the ElasticSearch/OpenSearch instance is slow, this can lead to projects being partially indexed.

Example Zendesk tickets:

• 646810
• 675347

The only option instance administrators have to get past this is to adjust the GitLab code manually and increase the timeout.

It would help if this setting would be exposed in the UI, to make it easier for administrators to adjust it if needed.