Expose WaitStrategy for Postgres

[WhiteTomX]

To avoid intermediate Errors as mentioned in #1148 we are using a custom wait strategy. Unfortunately we needed to duplicate the wait strategy of the Postgres Container as it is not exposed. It would be nice to have the possibility to add the postgres wait strategy when using custom wait strategies.

I'm not sure if it is enough to just expose the class, as it uses internal configuration. So we may need to think about it.

When this sounds useful I'm happy to make the required changes.

[HofmeisterAn]

We are not exposing the configuration. The suggested approach addresses the symptoms, but not the root cause. Container runtimes must handle port binding correctly, which resolves this issue as well as many others.