Remove special symbols from the histogram names in the PrHitsMonitors

Remove the special symbols in the PrHitsMonitors histograms.

@chasse: this MR only contains a few changes in histogram names since the special characters stopped us from being able to add them (easily) to the dashboard.

/ci-test --merge --platforms=x86_64_v2-centos7-gcc10-opt

added ci-test-triggered label

• [2021-09-07 14:32] Validation started with lhcb-master-mr#2849
• [2021-09-08 00:13] Validation started with lhcb-head-2#336

added lhcb-head-2 label

resolved all threads

merged

mentioned in commit 702cbd51

removed lhcb-head-2 label

added cleanup label

mentioned in issue Moore#316 (closed)

added Monitoring label