s3/rpc_server: install elasticsearch_mappings.json

s3/rpc_server: install elasticsearch_mappings.json

This was removed accidentally remvoed by
a7c65958a15149918415b7456d6f20ee8c9669d2 because the original code
only installed the json file if the mdssvc was built as module:

     if bld.SAMBA3_IS_ENABLED_MODULE('rpc_mdssvc_module'):
         bld.INSTALL_FILES(bld.env.SAMBA_DATADIR,
                           'mdssvc/elasticsearch_mappings.json')

Installing the json file should just depend on Elasticsearch support
being enabled, regardless of the removed module support.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14961

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Noel Power <npower@samba.org>
Autobuild-User(master): Noel Power <npower@samba.org>
Autobuild-Date(master): Fri Jan 28 10:22:31 UTC 2022 on sn-devel-184