fix: add pg username to migration job

[knorr3]

Description

After setting up chatwoot today, my instance was not able to start. I am using the built-in bitnami postgrsql db.
As it turned out, the db initialization (migration job) was stuck, because the pg_isready command in the init container didn't succeed. It just printed out no attempt, which suggests an invalid configuration (see https://www.postgresql.org/docs/current/app-pg-isready.html).

Solution

After adding the -U postgres parameter manually, the command exited with 0 and the migrations where able to run.