Emit a warning when an unknown geo strategy is passed in

[romseygeek]

Currently if you set a value other than term or recursive as the
deprecated strategy parameter on a geo_shape field, the mapper
will silently fall back to the recursive strategy. This commit changes
the parsing logic to emit a deprecation warning when this occurs,
informing the user that a) they're not getting the strategy they were
asking for, and b) this will turn into an error in the near future.

[elasticmachine]

Pinging @elastic/es-search (:Search/Mapping)

[romseygeek]

This is for 7.x only, as #63836 will make this an error in master.

[romseygeek]

This was handled by the backport of #63836