support per-pod ssh credential override

# Feature request

## Type

- [ ] - Enhancement - completely new feature
- [X] - Improvement - make what we have better

## Is your feature request related to a problem?

> A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

We have different groups building different images with different needs/desires for user account naming.

## Describe the solution you'd like

> A clear and concise description of what you want to happen.

I would like to be able to set the ssh creds on a per-pod basis by setting an annotation/label with the username and password to be used *for that pod* and overriding the defaults as set by the corresponding env vars.

## Additional context

> Add any other context or screenshots about the feature request here.