Merge pull request #66258 from aainscow/read_only_execs

osd/rados/rgw/cephfs: Modernize cls interface with compile time safety

Reviewed-by: Bill Scales <bill_scales@uk.ibm.com>
Reviewed-by: Radoslaw Zarzynski <rzarzyns@redhat.com>
Reviewed-by: Patrick Donnelly <pdonnell@redhat.com>
Reviewed-by: Adam Emerson <aemerson@ibm.com>