Support env vars in typed credentials

[matthiasbruns]

Description

While working on cosign, we discussed about how we can centralize credentials propagation from env vars.

I would see this as a stretch goal for the milestone but will keep it in here.

TODO: @matthiasbruns think about this

PR Comments
open-component-model/open-component-model#2344 (comment)

Done Criteria

• ...
• Code has been reviewed by other team members
• Analysis of existing tests (Unit and Integration)
• Unit Tests created for new code or existing Unit Tests updated
• Integration Test Suite updated (includes deletion of existing unnecessary Integration Test and/or creation of new ones if required)
• Enduser Documentation updated (if applicable)
• Internal technical Documentation created/updated (if applicable)
• Successful demonstration in Review