[Security Solution] ECS 1.11 Signal Mappings (#108764)

* Update signals mappings to include ECS 1.11

* Ensures no constant_keyword mappings
* Bumps index version by 1, since it was already bumped by 10 for 7.15
  in #106049

* Remove threat.indicator mappings from signals indices

Until the old, 7.14 enrichment mappings (which define threat.indicator
as nested) are in our rearview, we cannot add the official, non-nested
threat.indicator mappings as they'll conflict.