Add HashiCorp Vault Manager

[alberefe]

Implement credential management system with Hashicorp Vault integration. This provides automated secrets retrieval.

This relieves the user from hardcoding credentials in files and also automates the retrieval of api keys from pools in an automated way, optimizing speed when the program needs to rotate through several api keys or credentials to access different services in a row.

It follows the same idea of Bitwarden Manager class, but using other service.

The following are the contents of the PR:

Add Hashicorp manager (hc_manager.py)
Custom exception handling
Test coverage for the class functionality
Instructions of use

[alberefe]

Missed some things that are fixed now.

Poetry.lock was rebuilt, changelog included.

@jjmerchante @sduenas (mentioning you both cause I can't ask for reviews through the UI and I don't know if this got anywhere)

(sorry for delay was a crazy week)

[sduenas]

I think the PR looks ok but I'm suggesting some minor changes. Nothing related with how the code works.

[alberefe]

The changes have been done. I can't find a way to get that poetry.lock conflict out of the way. I have remade the poetry.lock file several times and tried this:

rm poetry.lock
poetry update
git add poetry.lock
git commit --amend

That apparently worked in the other PR but doesn't here?