[Maps] Decouple maps and maps_legacy config dependencies

[kindsun]

While working on #64668, it became increasingly evident how intertwined our map configurations are between legacy and new Maps. Here are a few things we might do to improve this situation:

• Audit current config schema and determine if all parts are used. Revise, add, and remove chunks as necessary
• Consider having entirely different configurations for maps_legacy and maps even at the risk of repeating values and remove maps dependency on maps_legacy
• Change map prefix to maps for consistency
• Maybe related to the last 2, store more new Maps configuration values under xpack.maps prefix
• Reconsider tilemap prefix
• Reconsider where tilemap configurations live since they're required for ServiceSettings

[nreese]

closed by #92918