Installing with an existing LetsEncrypt certificate and without using cert-manager

Is your feature request related to a problem? Please describe.

I've been using cert-manager to manage my certificates with the LetsEncrypt provider but I occasionally keep hitting their rate limits so I want to instead generate the certificate beforehand and use that with the actions controller webhook.
With https://github.com/actions-runner-controller/actions-runner-controller/pull/834 it seemed like this was possible but since that relies on the following local FQDN SANs so it would only work for self-signed certs

• webhook-service.actions-runner-system.svc
• webhook-service.actions-runner-system.svc.cluster.local

I might be missing something but if there's a way to do this currently I'd be really grateful to know it

Describe the solution you'd like

If there's a way to extend the current installation to install without cert-manager and using an existing certificate that would be great
(Managing the renewal of the certificate can be left to the user)

Describe alternatives you've considered

Considered using cert-manager with a cached certificate since hitting the LetsEncrypt rate limits seems to be a common issue but the issue doesn't seem to be making any progress

Additional context

The issue names no specific files, tests, or entry points; start by tracing the current webhook certificate installation and cert-manager configuration. Done means the controller can be installed without cert-manager while using a user-provided existing certificate, with certificate renewal left to the user.