graph-prottype: add timing gnuradio block

[wirew0rm]

Add timing related gnuradio blocks to gr-digitizers:

• hardware whiterabbit timing
• optional: timing block based on pps signal of gps module
• Software WR timing via UDP
  • gnuradio block that subscribes to udp service publishing events
  • mini-service to publish hardware events
• N.B. needs some standardisation effort w.r.t. minimum required key-value pairs and what goes into the 'trigger_meta_info' map (some stand-alone checker function)
• based on https://github.com/fair-acc/opendigitizer/issues/105, https://github.com/fair-acc/opendigitizer/issues/28 and https://github.com/fair-acc/graph-prototype/issues/210, https://github.com/fair-acc/gr-digitizers/blob/dev-prototype/blocklib/timing/include/timing.hpp