Make supplying the endpoints a bit smarter

[hatchan]

We should make it as easy for a user to supply the endpoints that they want to monitor. The only thing that is required is the host, all other components have some defaults:

• The protocol should only allow for http and https, where http is the default.
• The port should follow the default for the protocol, 80 for http and 443 for https.
• The path should default to /metrics if the path is empty. It should not be appended if a path is already there.

This should result in the following examples:

• am start 127.0.0.1: would result in http://127.0.0.1:80/metrics
  • All defaults
• am start https://127.0.0.1: would result in https://127.0.0.1:443/metrics
  • Non default protocol used
• am start localhost:3030: would result in http://localhost:3030/metrics
  • Non default port used
• am start localhost:3030/api/metrics: would result in http://localhost:3030/api/metrics
  • Non default path used, so use that instead
• am start localhost:3030/api/observability: would result in http://localhost:3030/api/observability
  • Non default path used, so use that instead (and do not add /metrics to it)

A user can also mix and match these: am start 127.0.0.1 https://localhost:3030/api/observability

NOTE: since we are adding the /metrics path when a path is not present in a endpoint it is not possible to have Prometheus scrape the root of a webserver. I think this is an acceptable limitation, since it makes the "normal" usage way more easy to use and users will not likely have their metrics in the / path.