Add Namecheap to the list of providers for ACME DNS-Authenticators

Problem/Justification
Currently, I am using Namecheap for all of my Domain Hosting / DNS. I would like to be able to use Namecheap as a provider for DNS Authentication for my TrueNAS instance.

Impact
This will provide additional resources / options to an existing function.

User Story
While I have a *.domain.com cert via LE for my domain, I am having trouble deploying it to my TrueNAS using multiple methods (deploy_truenas, tnas-cert, etc.). I was hoping to use the native UI feature to be able to deploy my certs instead of pushing one from an external source.