feat: implement SCIM handler for SCIM 2.0 compliance (#25572)

Rewrites the SCIM 2.0 user provisioning handler to be RFC 7644
compliant. Verified against an external IdP Okta.

Behavior is OPT IN

coderd/database/queries/users.sql

@@ -486,6 +486,18 @@ WHERE
 			name ILIKE concat('%', @name, '%')
 		ELSE true
 	END
+	-- Filter by exact username
+	AND CASE
+	  WHEN @exact_username :: text != '' THEN
+		  lower(username) = lower(@exact_username)
+	  ELSE true
+	END
+  	-- Filter by exact email
+  	AND CASE
+	  WHEN @exact_email :: text != '' THEN
+		  lower(email) = lower(@exact_email)
+	  ELSE true
+	END
 	-- Filter by status
 	AND CASE
 		-- @status needs to be a text because it can be empty, If it was