CI: Introduce cargo-semver-checks

This workflow looks for breaking API changes using popular
cargo-semver-checks tool.
This comit introduces it only for PRs. If PR breaks API, appropriate label is added, otherwise it is removed.
Future commits will also introduce jobs for tags pushes, to verify that we bumped versions correctly.

.github/workflows/semver_checks.yml

@@ -0,0 +1,36 @@
+# This workflow tests smver compatibilty.
+# For PRs it checks if PR makes any API breaking changes, and assings appropriate label if so.
+name: Semver checks
+
+on:
+  push:
+  pull_request:
+    branches:
+    - main
+    - 'branch-*'
+
+env:
+  CARGO_TERM_COLOR: always
+  RUST_BACKTRACE: full
+
+jobs:
+  semver-pull-request:
+    runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
+    permissions:
+      issues: write
+    timeout-minutes: 30
+    steps:
+    - uses: actions/checkout@v3
+    - name: Install semver-checks
+      run: cargo install cargo-semver-checks --no-default-features
+    - name: Verify the API compatibilty with PR base
+      id: semver-pr-check
+      run: cargo semver-checks --workspace --baseline-rev ${{ github.event.pull_request.base.sha }}
+      continue-on-error: true
+    - name: Remove breaking label on success
+      run: gh pr edit ${{ github.event.number }} --remove-label semver-checks-breaking
+      if: steps.semver-pr-check.outcome != 'success'
+    - name: Add breaking label on failure
+      run: gh pr edit ${{ github.event.number }} --add-label semver-checks-breaking
+      if: steps.semver-pr-check.outcome == 'success'