rgw: add hook for RGWOp subclasses to write custom metadata to ops logs

rgw: add hook for RGWOp subclasses to write custom metadata to ops logs

Adds a write_ops_log_entry method to the RGWOp class to allow it's
subclasses an opportunity to modify the request ops log entry.

Signed-off-by: Cory Snyder <csnyder@iland.com>
(cherry picked from commit be33b5d11e3b64356a0ef10a9795e6c33b7133dc)

Conflicts:
	src/rgw/librgw.cc
	src/rgw/rgw_lib.cc
	src/rgw/rgw_log.cc
	src/rgw/rgw_log.h
	src/rgw/rgw_lua_request.cc
	src/rgw/rgw_lua_request.h
	src/test/rgw/test_rgw_lua.cc

Cherry-pick notes:
- minor conflicts due to formatting and param changes