* Adds a wrapping "mappings.properties" around our extra mappings
* Spreads our other mappings similarly to ECS mappings
* Moves dynamic: false out of ECS mappings and into our main template
* Ensures we include 'threat.properties.indicator', since that's where
  our 'type: nested' declaration resides

This updated snapshot reflects the mappings changes that one will receive when
migrating/rolling over to a 7.13 alerts index.

The last released mappings update was elastic#92928, which bumped from 24 ->
25. The few unreleased updates since then have increased this by 1, but
since these changes are going out with 7.13 we are bumping by 10 _since
the last release_, in order to give "room" for minor releases.

This magic number represents "the number of mapped fields that begin
with 'host.geo.c' and, because this PR adds a mapping for
host.geo.continent_code, the test needed to be updated.