Restore pgAdmin support (PGAdmin CRD is inherited but non-functional)

Proposal

Percona's operator is forked from Crunchy Data's PGO, which ships a working PGAdmin controller. Percona still carries the inherited CRD shape, but there's no reconciler behind it - creating a PGAdmin CR is a no-op.

Before asking for it back, I'd like to understand the reasoning:

1. was dropping the pgAdmin controller during the fork intentional or simply code that didn't get ported over?
2. If it was a deliberate call, what drove it?

Use-Case

1. Teams using local PGAdmin and want to move to centrelized one
2. quick diagnostic access for on-call engineers who don't want to kubectl exec into a pod or open a psql tunnel just to run a query during an incident.
3. Teams migrating from Crunchy PGO who hit this gap during migration and have to bolt on their own pgAdmin deployment/Ingress by hand, per cluster, with no operator-managed lifecycle

Is this a feature you are interested in implementing yourself?

Maybe

Anything else?

The CRD scaffolding already exists in the codebase
so this is closer to "re-enable a controller" than "design new API surface"
unless we want to redisgn it and then I will be happy to help do so 😄

Start by locating the existing PGAdmin CRD scaffolding and comparing it with Crunchy Data's working PGAdmin controller; the issue names no specific files or tests. Determine whether the controller was intentionally omitted, with completion meaning that creating a PGAdmin CR is reconciled and its lifecycle is managed by the operator rather than being a no-op.