Add CI job to publish on crates.io when a release is tagged

This uses `katyo/publish-crates@v1`, which checks which crates have had
their versions bumped, and releases them on crates.io. While making sure
to publish dependencies first before the crate that depends on them.
This has apparently worked well in drm-rs.

Since subcrates are versioned differently, when we discussed this
earlier date-based tags names seemed best. So as @elinorbgr suggested,
this goes with `release-YYYY-MM-DD` as the tagging scheme. (The CI job
checks for tags prefixed with `release-`). I can't really think of
anything better than that.

So to release, we should be able to simply update the versions in
`Cargo.toml` files, update the changelog files, and tag a release.

The `publish-crates` action requires that all subcrates depends on the
latest version of any other crate in the repository. And it requires
that all crates with changes have a bumped version so they can be
released. This seems a bit annoying if we wanted to just release a
change to `wayland-backend`, for instance, but should help avoid
mistakes. Manually dealing with the releases for all the crates here,
without any automated checks, is error-prone.

The action here does a `dry-run` for all CI runs (and uses
`ignore-unpublished-changes` to not error if crates have changes without
already having their versions bumped). But disables `dry-run` when a
tag is pushed with the right format.

A `CRATES_TOKEN` secret will need to be added to the repository for this
to work.

.github/workflows/ci.yml

@@ -4,6 +4,8 @@ on:
   push:
     branches:
     - master
+    tags:
+      - 'release-[0-9]+-[0-9]+-[0-9]+'
   pull_request:
 
 jobs:
@@ -429,3 +431,24 @@ jobs:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./target/doc
           force_orphan: true
+
+  publish:
+    needs:
+      - format
+      - doc
+      - check-minimal
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v3
+      - name: Setup Rust
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+      - name: Publish crates
+        uses: katyo/publish-crates@v2
+        with:
+          registry-token: ${{ secrets.CRATES_TOKEN }}
+          args: --no-verify
+          dry-run: ${{ !(github.repository == 'Smithay/wayland-rs' && startsWith(github.ref, 'refs/tags/release-')) }}
+          ignore-unpublished-changes: ${{ !(github.repository == 'Smithay/wayland-rs' && startsWith(github.ref, 'refs/tags/release-')) }}