feat(enterprise/coderd): allow system users to be added to groups (#19518)

closes https://github.com/coder/coder/issues/18274

This pull request makes system users visible in various group related
queries so that they can be added to and removed from groups. This
allows system user quotas to be configured. System users are still
ignored in certain queries, such as when license seat consumption is
determined.

This pull request further ensures the existence of a
"coder_prebuilt_workspaces" group in any organization that needs
prebuilt workspaces

---------

Co-authored-by: Susana Ferreira <susana@coder.com>

coderd/database/dbauthz/dbauthz.go

@@ -487,6 +487,16 @@ var (
 					rbac.ResourceFile.Type: {
 						policy.ActionRead,
 					},
+					// Needs to be able to add the prebuilds system user to the "prebuilds" group in each organization that needs prebuilt workspaces
+					// so that prebuilt workspaces can be scheduled and owned in those organizations.
+					rbac.ResourceGroup.Type: {
+						policy.ActionRead,
+						policy.ActionCreate,
+						policy.ActionUpdate,
+					},
+					rbac.ResourceGroupMember.Type: {
+						policy.ActionRead,
+					},
 				}),
 			},
 		}),