Add secrets manager integration for credential retrieval

[alberefe]

Summary

• Add support for retrieving backend credentials from external secrets managers (Bitwarden, HashiCorp Vault) instead of passing them on the command line
• Credentials are fetched in BackendCommand._pre_init() and injected into parsed_args (user, password, api_token, email, etc.), which backends already consume via HTTP headers/session auth
• Enable secrets manager arguments (--secrets-manager, --item-name, --token-field, etc.) across 14 backends: bugzilla, bugzillarest, confluence, discourse, gerrit, git, github, gitlab, gitter, googlehits, groupsio, jenkins, rocketchat,
  stackexchange
• Add optional hashicorp-manager dependency group (hvac >= 2.3.0) in pyproject.toml
• Add documentation in README with usage examples for Bitwarden and HashiCorp Vault
• Add tests for the included functionality

[sduenas]

This looks promising. My main concern is that this only works using perceval from the command line and not as library. chronicler and mordred are two examples of perceval used as a library.

I think it would be better if perceval handles the access to the credentials on the backend and not in the backend command. What do you think?

[alberefe]

Closed it cause I'm making changes to adapt to what you said, also including changes to toolkit to modularize the functions and make it so the changes to perceval and others are minimal and everything stays inside toolkit as much as possible.