As we are moving to single type indices,
we need to address this change in security-related indexes.
To address this, we are
- updating index templates to use preferred type name `_doc`
- updating the API calls to use preferred type name `_doc`

Upgrade impact:-
In case of an upgrade from 6.x, the security index has type
`doc` and this will keep working as there is a single type and `_doc`
works as an alias to an existing type. The change is handled in the
`SecurityIndexManager` when we load mappings and settings from
the template. Previously, we used to do a `PutIndexTemplateRequest`
with the mapping source JSON with the type name. This has been
modified to remove the type name from the source.
So in the case of an upgrade, the `doc` type is updated
whereas for fresh installs `_doc` is updated. This happens as
backend handles `_doc` as an alias to the existing type name.

An optional step is to `reindex` security index and update the
type to `_doc`.

Since we do not support the security audit log index,
that template has been deleted.

Relates: elastic#38637