Bug 1623032 - upload flatpak in the "ship" phase, and push RCs to flathub beta. r=mtabara

Doing this in the ship phase instead of push lets us avoid shipping on
flathub before the actual release.

And, upload flatpaks for firefox release candidates to flathub's "beta"
channel so we can get feedback on them and QA can also get at them.

Differential Revision: https://phabricator.services.mozilla.com/D71919

taskcluster/ci/release-flatpak-push/kind.yml

@@ -15,7 +15,7 @@ kind-dependencies:
 job-defaults:
     description: Pushes Flatpaks onto Flathub
     run-on-projects: []  # to make sure this never runs as part of CI
-    shipping-phase: push
+    shipping-phase: ship
     treeherder:
         platform: linux64/opt
         kind: build

taskcluster/ci/release-secondary-flatpak-push/kind.yml

@@ -0,0 +1,38 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+---
+loader: taskgraph.loader.transform:loader
+
+transforms:
+    - taskgraph.transforms.release_deps:transforms
+    - taskgraph.transforms.release_flatpak_push:transforms
+    - taskgraph.transforms.task:transforms
+
+kind-dependencies:
+    - release-flatpak-repackage
+
+job-defaults:
+    description: Pushes Flatpaks onto Flathub
+    run-on-projects: []  # to make sure this never runs as part of CI
+    shipping-phase: ship  # ship-rc phase
+    treeherder:
+        platform: linux64/opt
+        kind: build
+        tier: 2
+    worker-type:
+        by-release-level:
+            production: scriptworker-k8s/gecko-3-pushflatpak
+            staging: scriptworker-k8s/gecko-1-pushflatpak
+    worker:
+        implementation: push-flatpak
+        channel:
+            by-release-type:
+                release-rc: "beta"
+                default: "mock"
+
+jobs:
+    firefox-rc:
+        shipping-product: firefox
+        treeherder:
+            symbol: Flatpak(push-beta)

taskcluster/docs/kinds.rst

@@ -329,6 +329,11 @@ release-secondary-snap-push
 Performs the same function as `release-snap-push`, except for the beta channel as part of RC
 Releases.
 
+release-secondary-flatpak-push
+------------------------------
+Performs the same function as `release-flatpak-push`, except for the beta channel as part of RC
+Releases.
+
 release-notify-av-announce
 --------------------------
 Notify anti-virus vendors when a release is likely shipping.