Add X509 client certificate credential type

[primasolutions-fr]

What feature do you want to see added?

Hi,
One of the last credential not provided by the Hashicorp Vault Plugin is the X509 client certificate. I'd be very happy to have it implemented.
This kind of credential is used to store Docker's remote API client certificates, by example.

Upstream changes

No response

Are you interested in contributing this feature?

I'm far from a developer guy, but would be happy to help testing.