feature: Introduce secrets function

[saikonen]

introduces a get_secrets function that exposes the same capabilities as the @secrets decorator, but returns them as a dictionary instead of setting environment variables.

The use case is to make accessing secrets possible in user-code as well.

example:

@step
def start(self):
    secrets_dict = get_secrets(sources=["secret_source"], role="IAM_role_for_accessing")
    
    for secret_spec, contents_dict in secrets_dict.items():
         pass # do something with the fetched secrets

[nflx-mf-bot]

Testing[888] @ 252012d