Bump Magnum Cluster API to 0.27.0

Add extra tool for bumping MCAPI by simply running:

> just bump-magnum-cluster-api

Change-Id: Ifbcc00b3012d14cbf2304390d999a8e425eeb6bb
diff --git a/justfile b/justfile
new file mode 100644
index 0000000..e79c16f
--- /dev/null
+++ b/justfile
@@ -0,0 +1,5 @@
+default:
+  just --list
+
+bump-magnum-cluster-api:
+  cargo run --bin mcapibumper