Backport to 13_2_X based on PR cms-sw#42634

Hack to get the zdcEtSums into the simCaloGtDigis collection:

Mass update for Upgrade tree and update to README for clearer instruc…

…tions + modified for combining ZDC EtSums into one object

Collapsed ZDCP and ZDCM outputs of the L1TZDCProducer into a single E…

…TSum; P and M now distinguished by kZDCP and kZDCM EtSum type id defined in the data format - also altered the test L1TZDCAnalyzer and the l1ZDCProducerTest.py file, checked the outputs looked unchanged when running with this update

Mass update for Upgrade tree and update to README for clearer instruc…

…tions + modified for combining ZDC EtSums into one object

Updated README for git tag zdcL1T_latest to avoid future need for REA…

…DME updates

Updated README for more info that was missing in build + fixed a bunc…

…h of typos

Still fixing README

Updated README file to fix readability and add some common debug info

Small fixes for LUT + reduced bx from 10 to 5 (centered on bx 4, posi…

…tion of peak, for 2, 3, 4, 5, 6 in zdc output) - Analyzer nBX reduced to 5 (hardcoded), also LUT in caloParams now points to what we pull in under L1Trigger/L1TZDC/data - this is the set of changes for incrementing to v0.2.0