ci: add conform workflow and configuration

Signed-off-by: Marvin Beckers <mail@embik.me>

.conform.yaml

@@ -0,0 +1,37 @@
+policies:
+  - type: commit
+    spec:
+      header:
+        length: 89
+        imperative: true
+        case: lower
+        invalidLastCharacters: .
+      dco: true
+      spellcheck:
+        locale: US
+      conventional:
+        types:
+          # build system, releases
+          - "build"
+          # changes with no functional effect (e.g. updating dependencies)
+          - "chore"
+          # GitHub Actions
+          - "ci"
+          # Documentation
+          - "docs"
+          # Unit and integration tests
+          - "test"
+        scopes:
+          # everything related to cargo configuration and dependencies
+          - "cargo"
+          # all current subcommands in kbs
+          - "import"
+          - "label"
+          - "list"
+          - "move"
+          - "prune"
+          - "remove"
+          - "shell"
+          - "use"
+          - "version"
+        descriptionLength: 72

.github/workflows/conform.yaml

@@ -0,0 +1,24 @@
+---
+name: Commit Conformance
+on:
+  pull_request:
+    branches: ["main"]
+
+jobs:
+  signoff:
+    runs-on: ubuntu-latest
+
+    if: github.event_name == 'pull_request'
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.sha }}
+
+      - name: Setup main branch without switching current branch
+        run: git fetch origin main:main
+
+      - name: Conform Action
+        uses: siderolabs/conform@v0.1.0-alpha.29
+        with:
+          args: "enforce --base-branch=main"