[RTA/DPA BW Tests] Introduce new hlt2_and_spruce_bandwidth test

Related to lhcb-core/LHCbNightlyConf!1140 (merged) + lhcb-core/LHCbPR2HD!273 (merged)

Introduces PR/Moore_hlt2_and_spruce_bandwidth tests and label. cc @rjhunter
The jobs are, in essence, a spruce job on the full-stream output of a nominal hlt2 job that has ran locally.
Outputs all the information/pages to be expected from both jobs plus some human-readable index pages / messages to be used later by the PR TestHandler.

Example output files can be found under /eos/lhcb/user/l/lugrazet/public/BWTesters/chained-30-Jan/.
NB: To reduce 'strain' from JIT Functor Compilation, running a much reduced Hlt2 job locally so it's enough to verify that the test infrastructure is working but the output might seem odd.

While testing, found that we ignored EVTMAX if reading in evtmax from metadata (i.e. for latest and chained sprucing jobs). Fixed now !374 (diffs).

Also made some renaming of existing arguments for improved clarity. (see: comments on the opaque-ness of spruce_latest & spruce_chained !374 (comment 7508385) and !374 (comment 7508747) ToDo:

• Review @rjhunter
• Downstream changes