Horizon DB migrations execute on non-ingesting instances

[jacekn]

What version are you using?

Horizon 2.21.0

What did you do?

Horizon 2.21.0 was deployed and it run migrations on instances that had ingesting disabled.

What did you expect to see?

I expected migrations to only run on instances with ingestion enabled.

What did you see instead?

Migrations run on non-ingesting instances and those did not have write access to the database so failed.

@bartekn said that we do check it but only when migrations are done via --apply-migrations flag not db migrate up command. https://github.com/stellar/go/pull/3586/files