dirauth: Add stats to MetricsPort
The following should be provided to the MetricsPort so directory authority can track a bit better their current state. This is especially useful in case of DDoS.
- Total count DirPort connections
- Total count ORPort connections
- Total count BEGIN_DIR (ORPort)
- Total count of compressed methods used for directory request
- Total count consensus by flavor served
- Total count descriptors by flavor served
- Total count of directory requests