[Security Solution] Add host.os.name.caseless mapping and runtime fie…

…ld (elastic#111455)

* Add host.os.name.caseless field and runtime field

* Tests

* Only add backwards compatibility mappings to old indices by version

* Always update aliases_version field even if there are no compat mappings

* Add test for newest index version

* More comments

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>