Merge 21.0.100 into 21.3 branch

This commit merges nearly all the changes that were made to the 21.0 branch between the release release/21.0.100 and the previous release release/21.0.99.

Below is a full list of merge requests that were accepted between these two tags:

• !25081 (merged) : Add SimulateCavern simFlag, which can be used independently of CavernBG and cosmics simulation
• !25077 (merged) : Fix a problem of HnlSkimmingTool and code cleanup (ATLDHNL-21)
• !25066 (merged) : Sweeping !25041 (merged) from 21.2 to 21.0.
• !25053 (merged) : Added q440 test to TCT for pileup check
• !25036 (merged) : Add bunch patterns for Run 3 tests
• !25026 (merged) : Revert changes of SCT_FrontEnd.cxx of MR !20456 (merged) to fix ATLASSIM-4227
• !24990 (merged) : Add an ART test for qball digitization
• !24429 (merged) : Inner Detector Alignment Performance Monitoring to use MCP muon tagging
• !24967 (merged) : Fix beam conditions propagation for the standard digitisation (ATLPHYSVAL-619)
• !24920 (merged) : Make EventAuxInfo_v1 data members public
• !24921 (merged) : Set ParticleSimWhiteList to True by default in SimFlags
• !24931 (merged) : Sweeping !24861 (merged) from master to 21.0.
• !24796 (merged) : Low energy particle removal for FCS
• !24657 (merged) : Fix for test_athena_G4AtlasCosmic (ATLASSIM-4186)
• !24664 (merged) : DataHeader_p6 reading
• !24567 (merged) : Extra SM mesons
• !24627 (merged) : Sweeping !24584 (merged) from 21.3 to 21.0.
• !20456 (merged) : Sweeping !20374 (merged) from 21.3 to 21.0.SCT RDO updates for overlay MC (ATLASSIM-3903)
  Removed from sweep due to incompatibility:
• !24737 (merged) : Fix for broken HepMcParticleLinks seen during MDT_Digitization (ATLASSIM-4225)

Link to the full diff between release/21.0.100 and release/21.0.99 is available at https://gitlab.cern.ch/atlas/athena/compare/release/21.0.99...release/21.0.100