Backfill Elastic migration dictionary records

What does this MR do and why?

Backfill Elastic migration dictionary records and adds a spec to check that every migration has a corresponding dictionary record.

Related to !125265 (merged)

Screenshots or screen recordings

If some migrations don't have a dictionary record, the spec will fail with:

How to set up and validate locally

Execute spec ee/spec/elastic/docs_spec.rb

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #414674 (closed)