feat(balance): update military outposts

[chaosvolt]

Purpose of change

This starts some belated updates to military outposts, continuing on from the balancing plans mentioned back when I tackled military bases.

Describe the solution

1. Converted the ground areas to use t_region_groundcover instead of old-school terrain selection.
2. Defined fill_ter to cut down on t_floor spam.
3. Converted the interior monster spawns to use monstergroups instead of placing a random selection of specific monsters. In this case went with GROUP_MAYBE_MIL, which will become zombie-only as noted below.
4. Converted GROUP_MAYBE_MIL to have only military zeds instead of robots, and increased the variety of potential spawns considerably.
5. Added a few spawns of GROUP_ROBOTS_MIL outside and in the more secured rooms.
6. Swapped the exterior doors from simply closed metal doors to pickable locked metal doors, since the monstergroup used now can include feral soldiers who can open doors.
7. Sanity-checked and toned down the cornucopia of loot in the outpost lockers, moving them into a better-secured area in the outpost instead of squarely in the middle (swapping the tables and counters into that area instead). In exchange however, increased the variety of groups that can spawn there a bit, in particular adding a secondary locked-up room where the energy weapon items spawn now, also capable of spawning power armor and related electronics.
8. Split the two outpost variants up into two separate overmap specials and added roof levels to both, finally fixing the issue where the plutonium generators let light in from above. This also makes it easier to add a second floor later on. :3
9. Removed yet another hacky override from No Hope blyat
10. Added ELECTRIC_GRID flag to outposts now that they have roofs.

Describe alternatives you've considered

Working on the misc idea of adding a second floor to these locations, converting them to use mapgen pallets, and moving the file to the military subfolder now. I was thinking start with the basic overhauls first.

Testing

1. Checked affected files for syntax and lint errors.
2. Load-tested in compiled test build and spawned them in, checking layouts look as intended.
3. Spawned in again after adding the computer lock to the power armor rooms, confirmed with 10 computer skill that unlocking them works as intended.

Screenshots, Before:

Screenshots, After:

"after" screenshots are a lil different from final layout since I swapped in some metal shutter doors and computer consoles for the power armor and electronics storage room.

Additional context

Checklist