Add secrets manager integration for credential retrieval

[alberefe]

Integrate Perceval with external secrets managers (Bitwarden, HashiCorp Vault) so credentials can be resolved at runtime instead of being passed as plain-text CLI arguments.

• Add --secrets-manager, --item-name, and provider-specific CLI flags
  to BackendCommandArgumentParser
• Add _pre_init() and _build_manager() in BackendCommand to orchestrate credential resolution via grimoirelab-toolkit's resolve_credentials()
• Enable secrets manager support on 14 backends
• Add hvac as optional dependency group
• Usage in README

[alberefe]

I'll be fixing this later please wait before you check so every test and dependency is working fine!

[sduenas]

Please check my initial comments. Also, my concern is this only makes perceval work if you use the backend command but not the library. Please evaluate if it makes sense to integrate it within fetch or other methods, or if on the other hand, developers should use grimoirelab toolkit instead.

[sduenas]

Please fix the lint errors and add unit test for this functionality.

[alberefe]

Getting those errors cause I think it's importing an old version of Toolkit from before it had the las PR changes, is that correct? Not sure how to deal with that or if I'm even correct, but not sure what to do with it.

[sduenas]

Getting those errors cause I think it's importing an old version of Toolkit from before it had the las PR changes, is that correct? Not sure how to deal with that or if I'm even correct, but not sure what to do with it.

We fixed it in #900. Please rebase your branch.

[alberefe]

Please fix the lint errors and add unit test for this functionality.

Please fix the lint errors and add unit test for this functionality.

Linting errors should be fixed and made tests for the env functinoality.

[sduenas]

Please check my comments. The tests fail because hvac is not installed.

[alberefe]

Fix the poetry.lock file (needed to update some packages) and the testing now properly tests perceval functioning and not toolkit.

[jjmerchante]

Overall, it looks good to me. Just some minor changes

[alberefe]

So, I fixed the things you commented, but I am not sure how to proceed with the poetry.lock conflict. I updated poetry to match the version of main, but now I'm getting other conflicts and not sure if leaving it to you. Not fully understand what the problem is.

[jjmerchante]

LGTM

[sduenas]

Everything looks good to me now. However, would you mind to move the documentation from the README to a file on /docs/perceval? I think it's too long for the readme file. You can leave a brief description of its usage and the rest, move it to a file there. You can also link the file from the README for those who need more info.

[alberefe]

Created a new docs file and linked to it from the README.md.

[sduenas]

LGTM