Draft: Decomposed db migrate reset test decomposed

What does this MR do and why?

Testing for !77044 (merged) with a decomposed pipeline

In the db:migrate:reset decomposed job's raw output, we can see the following, supporting that this job executed correctly:

• Using decomposed database config (config/database.yml.decomposed-postgresql) indicates that the decomposed database config was swapped in

• By searching for InitSchema (or any other migration) we can see that they were executed twice - once against each database.