XML: upgrade-2.10.xsl: rsc op instance_attrs [1/2]: meta-like requires

Also prevent "requires" from per-operation instance_attributes in
pacemaker-3.0.rng, with a prospect to lift that again in the immediately
following version 3.1, which would make for this arrangement:

• 3.0 that serves as a "transitional" version, denotes "right after upgrade from 2.x" phase and is strict about enumerated instance attributes of resource's operations (and perhaps elsewhere) that were previously (with pre-3.0 schema) possibly ambiguous -- the upgrade transformation (upgrade-2.10.xsl) makes them no longer occurring like that so it is valid to forbid them in the upgrade's target schema version (against which the outcome will be validated), but that's just a midstep towards subsequent and more relaxed...

• 3.1 that lifts the restrictions imposed on instance attributes (which are meant to be dictated by the resources, i.e., the metadata of respective agents) in 3.0 (but retains those previously imposed on meta attributres, since these are fully under pacemaker's autonomy) -- main purpose is not to occupy the namespace of instance attributes artificially with banned keys just because of the unfortunate dualities/discrepancies in the past (hence dropping the need to document such a kludge, etc.), at least since this first schema in 3.x line to be practically used

Such an arrangement enforces correctness of upgrade-2.10.xsl (ensures
the result won't cross the expected boundaries incl. said interim
additions) and makes for a good "sanity" heuristic in case one would
bump "validate-with" field in the CIB to "3.0" from any older version
when modifying manually.