packit: Enable RPM builds and Fedora testing

Teach `make dist-gzip` to print the tarball name as last line, and use
it as `create-archive` action.

Add a `make print-version` command which packit can use. The builtin
default only works if there is at least one git tag, which is not the
case for starter-kit (which is never released).

packit.yaml

@@ -0,0 +1,19 @@
+# Enable RPM builds and running integration tests in PRs through https://packit.dev/
+# To use this, enable Packit-as-a-service in GitHub: https://packit.dev/docs/packit-as-a-service/
+# See https://packit.dev/docs/configuration/ for the format of this file
+
+specfile_path: cockpit-starter-kit.spec
+actions:
+  post-upstream-clone: make cockpit-starter-kit.spec
+  # reduce memory consumption of webpack in sandcastle container
+  # https://github.com/packit/sandcastle/pull/92
+  # https://medium.com/the-node-js-collection/node-js-memory-management-in-container-environments-7eb8409a74e8
+  create-archive: make NODE_OPTIONS=--max-old-space-size=500 dist-gzip
+  # starter-kit.git has no release tags; your project can drop this once you have a release
+  get-current-version: make print-version
+jobs:
+  - job: tests
+    trigger: pull_request
+    metadata:
+      targets:
+      - fedora-all