Support cert and proxies in Vault client session setup

[vuonghoangbntt]

Description

Previously, only the 'verify' option was handled when creating the session for the Vault client.
This change extends it to also support 'cert' (client certificates) and 'proxies' passed via kwargs ensuring compatibility with the hvac client, which reads these values from the session. (HVAC Adapter)

This allows advanced connection configurations like mutual TLS authentication and proxy routing
while preserving retry logic.

Updated tests to cover proxies and client cert cases.

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[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.