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

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information