Migrate issuable states to integer patch 1 of 2

What does this MR do?

Migrates issues/merge_requests state column from string to integer.
This migration will require two releases to avoid downtime.
A second merge request will be opened as soon as this one gets merged.

First release(this merge request)

1. Add a state_id column to issues and merge requests tables
2. Schedule a background migration that will populate state_id column with new values

Second release(next merge request)

1. Adds new indexes to state_id column
2. Add the code which uses the new state_id column
3. Removes old state column with a post deployment migration

What are the relevant issue numbers?

closes #51789 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer