Add environment variable registration mechanism for ephemeral pods

[kidgilson]

Is your feature request related to a problem? Please describe.
Ephemeral pods launched by Kanister need to have environment variables injected based on the outer OS environment variables (parent pod that launched these ephemeral pods) or based on static environment variables that need to be added.

The possible set of conditional environment variables needs to be registered and if found in the outer OS then should be injected. The static environment variables, when registered, should always be added to the container environment variables.

Describe the solution you'd like
Add an ephemeral package which has a registration scheme for environment variables which can be used outside Kanister to register which environment variables you'd like injected.

Additional context
This helps to get the correct FIPS required environment variables into the ephemeral pods to ensure the crypto backend is started in FIPS mode.

[github-actions]

Thanks for opening this issue 👍. The team will review it shortly.

If this is a bug report, make sure to include clear instructions how on to reproduce the problem with minimal reproducible examples, where possible. If this is a security report, please review our security policy as outlined in SECURITY.md.

If you haven't already, please take a moment to review our project's Code of Conduct document.