We have an open question of how long does it take for each target
pool to have the state retrieved from all participating elements.
This commit starts by providing insight into this.
client_golang was updated to support full label-oriented telemetry,
which introduced interface incompatibilities with the previous
version of Prometheus. To alleviate this, a general fetching and
processing dispatching system has been created, which discriminates
and processes according to the version of input.
