Vault PKI secrets support

[dbnicholson]

What feature do you want to see added?

Currently the plugin provides certificate credentials where the implementation fetches a certificate out of Vault's K/V secret storage. It would be really cool if it could also fetch from Vault's PKI secret engine where certificates are issued on the fly. This would allow Jenkins to use ephemeral, short TTL client certificates instead of issuing a long lived certificate and storing it in Vault.

Upstream changes

No response