Support for custom CA certificates

**Describe the problem you have/What new integration you would like**

It would be nice to have a configuration option to include custom Certificate Authority certificates in the ESPHome container.

**Please describe your use case for this integration and alternatives you've tried:**

I need to be able to add a custom CA certificate to the ESPHome container so that it may connect to my local Git server. I currently do this by `docker cp` the cert into the container and then `update-ca-certificates` in the container shell.

**Additional context**

I have a homelab that does not have a public domain name. I have ESPHome as an addon in my Home Assistant instance. I also have an internal Git server secured by a TLS cert of my own CA. If I want to use ESPHome's package feature I need to be able to trust my own CA so that the container may checkout my code from my Git server and complete firmware builds.