Draft: Create gitlab-database-index-repair gem

What does this MR do and why?

Create gitlab-database-index-repair gem

This MR creates a skeleton for the gitlab-database-index-repair gem.

References

• Add a command for reindexing a system broken by... (omnibus-gitlab#6974)
• Database index corruption caused by a change in... (&8573)

How to set up and validate locally

MR acceptance checklist

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