Step 1: Move Elasticsearch admin options from Integrations to top level

⚠ This issue is not released yet, all the involved MRs are merged into !17230 (closed) and the remainder of this work is being tracked in &1769.

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Problem to solve

We want to make Elasticsearch options available from top level Admin area.

So instead of:

Admin area > Integrations > Elasticsearch

we want to have:

Admin area > Elasticsearch

Additional tasks:

• Add ability to show/hide AWS credentials area via checkbox (frontend)
• Make sure the "start indexing" button works here too (https://gitlab.com/gitlab-org/gitlab-ee/issues/12712)

Further details

See epic for details: &1769

Proposal

1. 
2. 
3. 

The copy on the submit button should be "Save changes" as per today.

The title on the left sidebar, since we don't have multiple indexes yet, should be "GitLab Index".

Postponed for step 2

1. 

Links / references