Add HLT FCal-based forward gap hypo and test chains (ATR-24707)

This MR adds the HLT hypo for selecting events with forward gaps calculated from FCal activity (upper cut on FCal ET, one-sided or on both sides). A few test chains with this functionality are included in the dev HI menu. For these to actually work, also a corresponding chain configuration via the HeavyIon slice is added. The FCal-based gap calculation is similar to what was used in rel 21, where the forward gap calculation was implemented as a special instance of the ultra-central hypo.

Tagging @qhu for comments on the HI part (implementation and configuration). Since !57170 (merged) also modifies the dev HI menu, which one should go first?

Tagging also @khoo to please confirm that the changes to the menu generation/configuration make sense (should not be breaking anything for pp).