Add Ability to Reload MySQL Configuration File

[celestialorb]

I'm currently using a Vault sidecar injector to inject the .my.cnf configuration file into the pod and it would be nice if I could inform the exporter itself to reload that file. This could be done by having the exporter itself watch the file for changes, or this could be done in similar fashion to how Prometheus handles it: with a configuration reload HTTP endpoint.

[SuperQ]

I think a reload endpoint or SIGHUP would be reasonable.