Allow access-control "write" metadata to say "true" for read-only attributes

Revert behavior introduced in WFLY-2029.

The problem is "access-type" relates to how an attribute is handled after the resource is added; e.g. for the write-attribute op. It does not govern whether it is set by the user as part of resource add.

OTOH, the access-control "write" setting covers both add and post-add modification.

Mixing the two leads to things like the console not allowing the Maintainer role to set non-sensitive attributes in the form used for adding resources, e.g. https://bugzilla.redhat.com/show_bug.cgi?id=1017062.