feat(helm): configure MIW Helm chart to use pgadmin4 subchart

[pmoscode]

Description

This PR configures the pgadmin Helm chart for usage inside the MIW Helm chart as part of the series of PRs to implement issue #147

Pgadmin is disabled by default, so it has to be enabled / configured in the values.yaml.
A default user / password is set. (The pgadmin chart itself sets also a default password, which is overwritten here)

Beside that, the MIW Postgresql DB is preconfigured and can be instantly used. You just have to provide the password for the DB.
This can be addressed in a new issue / PR.

Pre-review checks

Please ensure to do as many of the following checks as possible, before asking for committer review:

• DEPENDENCIES are up-to-date. Dash license tool. Committers can open IP issues for restricted libs.
• Copyright and license header are present on all affected files

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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[pmoscode]

These errors are due to the need to split up the original PR to avoid IP check.
Hence, the PRs are additive and these errors will be fixed automatically with the previous PR completing the missing things.

I.e. please merge the PR anyway and let the previous one be merged timely, too.