feat(credential): implement the secret process (#7882)

[Gabriel Pezé (gabriel-peze)]

Proposed changes

• Add the process to retrieve the credentials and convert them into files and vars envs by credential types

Related issues

• Relates #7882

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality
• For bug fix -> I implemented a test that covers the bug

[Christophe Melchior (Kakudou)]

The implementation have been done and tested in both stratus (OpenAEV-Platform/injectors#472) and prowler (OpenAEV-Platform/injectors#471).

I've added a selector 'credentials' to the contract, allowing to switch from the new creds manager to the old manual way:

i've created a creds for aws:

and tested it in various prowler contracts:

and it works: