Squash agent version reporting in boostx stats

[jacobheun]

boostx stats currently counts all unique agent versions and displays them as a list in the output, however, this can end up being a lot of reported versions if folks are running off certain commits on the main branch (which is common).

We could probably squash this result into a more succinct summary by trimming the agent version after the first +. This does result in us getting less information about the agent versions, but we could probably add a verbose summary flag if we wanted expanded results.

Current Example

Agent Versions:
  boost-1.6.1+git.4931e18: 31
  boost-1.6.1+git.4931e18.dirty: 3
  boost-1.6.1+git.4931e18e: 3
  boost-1.6.1+git.d31c62f.dirty: 3
  boost-1.6.1-rc1+git.a1e7cc1: 1
  boost-1.6.1-rc1+git.e25ff0d: 2
  boost-1.6.2-rc1+git.0b5cf47: 1
  boost-1.6.2-rc1+git.0b5cf47.dirty: 1
  boost-1.6.2-rc1+git.0b5cf477: 1
  boost-1.6.2-rc1+git.2172161: 1
  boost-1.6.2-rc1+git.2172161.dirty: 1
  boost-1.6.2-rc2+git.3403cbb: 5
  boost-1.6.2-rc2+git.3403cbb.dirty: 3
  boost-1.6.2-rc2+git.ae99ff4: 1
  boost-1.6.2-rc2+git.d8825f7: 1
  boost-1.7.0-rc1+git.ac6f82e: 1
  ...

Proposed Example

Agent Versions:
  boost-1.6.1: 40
  boost-1.6.1-rc1: 3
  boost-1.6.2-rc1: 5
  boost-1.6.2-rc2: 10
  boost-1.7.0-rc1: 1
  ...