Comment changeset status in PRs (#625)

* Initial implementation

* Fix

* fix

* fix

* Make it look nicer

* Update docs

* Rename to pr-status-comment

* Remove outputs

* Update path

* update name

* Checkout PR in a detached worktree (#626)

Co-authored-by: bluwy <bjornlu.dev@gmail.com>

* Move comment to separate job

* Loosen event requirement

* Update

* Apply suggestions from code review

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

* Use TLA

* use using

* Remove test log

---------

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

src/pr-status/template.ts

@@ -0,0 +1,30 @@
+import { getChangedPackagesSinceRef } from "@changesets/git";
+import { humanId } from "human-id";
+
+export function getNewChangesetUrl(
+  headRepoUrl: string,
+  headRef: string,
+  templateContent: string,
+) {
+  const fileName = humanId({ separator: "-", capitalize: false });
+  return `${headRepoUrl}/new/${headRef}?filename=.changeset/${fileName}.md&value=${encodeURIComponent(templateContent)}`;
+}
+
+export async function getNewChangesetTemplateContent(
+  cwd: string,
+  baseRef: string,
+  prTitle: string,
+) {
+  const changedPackages = await getChangedPackagesSinceRef({
+    cwd,
+    ref: baseRef,
+  });
+
+  return `\
+---
+${changedPackages.map((p) => `"${p.packageJson.name}": patch`).join("\n")}
+---
+
+${prTitle}
+`;
+}