Add elastic rake tasks to check group indexing status

What does this MR do and why?

This merge request adds support for tracking and monitoring Elasticsearch indexing status for GitLab groups, similar to the existing functionality for projects.

The changes introduce new tools to help administrators see which groups haven't been indexed yet and check the overall indexing progress for group data (like group wikis). This includes new command-line tasks that show indexing percentages and list groups that still need to be processed.

The code also improves how the system determines which projects and groups should be indexed when Elasticsearch indexing is limited to specific namespaces, making the logic more consistent and reusable across different parts of the application.

Additionally, the changes update documentation to clarify that indexing status only considers repository data (code, commits, and wikis) and not other content like issues or merge requests. Some code quality improvements were made by removing a file from a style guide exception list and updating how the system checks if it's running on GitLab.com.

It adds two rake tasks similar to projects

• index_groups_status
• groups_not_indexed

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Query plan

https://console.postgres.ai/shared/e23ad0d7-2c3d-4c97-ac07-9f9d11dccf07

Related to #420656