MEDIUM: stick-tables: add a new stored type for glitch_cnt and glitch_rate

MEDIUM: stick-tables: add a new stored type for glitch_cnt and glitch_rate

This adds a new pair of stored types in the stick-tables:
  - glitch_cnt
  - glitch_rate

These keep count of the number of glitches reported on a front connection,
in order to decide how to act with a badly defective client or a potential
attacker. For now nothing updates these counters, but all the infrastructure
needed to configure, update and retrieve them was added, including the doc.

No regtest was added yet since they're not filled yet.