Ensure that enabling AutoConfig sets the tls configurator properly
This also refactors the TLS configurator a bit so the naming doesn’t imply only AutoEncrypt as the source of the automatically setup TLS cert info.
Most of the groundwork was laid in previous PRs between adding the cert-monitor package to extracting the logic of signing certificates out of the connect_ca_endpoint.go code and into a method on the server.
This also refactors the auto-config package a bit to split things out into multiple files.
There were several PRs that while all passed CI independently, when they all got merged into the same branch caused compilation errors in test code.
The main changes that caused issues where changing agent/cache.Cache.New to require a concrete options struct instead of a pointer. This broke the cert monitor tests and the catalog_list_services_test.go. Another change was made to unembed the http.Server from the agent.HTTPServer struct. That coupled with another change to add a test to ensure cache rate limiting coming from HTTP requests was working as expected caused compilation failures.
The fallback method would still work but it would get into a state where it would let the certificate expire for 10s before getting a new one. And the new one used the less secure RPC endpoint.
This is also a pretty large refactoring of the auto encrypt code. I was going to write some tests around the certificate monitoring but it was going to be impossible to get a TestAgent configured in such a way that I could write a test that ran in less than an hour or two to exercise the functionality.
Moving the certificate monitoring into its own package will allow for dependency injection and in particular mocking the cache types to control how it hands back certificates and how long those certificates should live. This will allow for exercising the main loop more than would be possible with it coupled so tightly with the Agent.
