ATR-28969: L1Menu diff test to enforce frozen L1Topo FW
During operations (i.e. outside YETS), the L1Topo firmware is frozen, and changes are restricted to bugfixes. Redefinitions of L1Topo algorithms in the L1Menu python may imply firmware changes, which we wish to avoid.
This ART test generates a new L1 menu with the latest athena python, and then performs a diff against a reference L1Menu held in the TrigP1Test package. Alternative naming scheme proposals as welcome... I thought a generic name was preferable, and was tempted to insert the source release in the json blob but it's probably better to use the original json and mark the athena version in the commit (though it'll be squashed, it's accessible from the associated MR).
The test runs in a few seconds, so should be viable to put in CI.
Menu experts should run this check when making changes to the L1 menu.