Add select-mode, version, pack and publish sub-actions (#656)

* Add select-mode, version, and publish sub-actions

* Rename

* No github-token needed for select-mode for now

* extend select-mode with publish-plan check and upload

* Rename base-branch to pr-base-branch

* add `pack` subaction

* `--from-pack` support in the publish subaction

* rename CLI arg

* update rolldown config

* rename pack dir input/output

* tweak retendion days

---------

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

pack/README.md

@@ -0,0 +1,3 @@
+# changesets/action/pack
+
+TODO

pack/action.yml

@@ -0,0 +1,15 @@
+name: Changesets - Pack
+description: Pack publishable packages into tarballs
+runs:
+  using: node24
+  main: ../dist/pack.js
+inputs:
+  publish-plan-artifact-id:
+    description: "Artifact id for a publish plan generated by the select-mode subaction"
+    required: false
+outputs:
+  pack-dir-artifact-id:
+    description: "Artifact id for the packed output directory"
+branding:
+  icon: package
+  color: blue