Add Code Coverage GH action

.github/workflows/coverage.yml

@@ -0,0 +1,50 @@
+name: Code Coverage
+
+on:
+  pull_request:
+  push:
+    # trying and staging branches are for BORS config
+    branches:
+      - trying
+      - staging
+      - main
+
+permissions:
+  contents: read
+  issues: write
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  coverage:
+    # Will not run if the event is a PR to bump-meilisearch-v* (so a pre-release PR)
+    # Will still run for each push to bump-meilisearch-v*
+    # Will not run if the actor is Dependabot (dependabot PRs)  
+    if: github.event_name != 'pull_request' || !startsWith(github.base_ref, 'bump-meilisearch-v') ||  github.actor != 'dependabot[bot]'
+    runs-on: ubuntu-latest
+    name: Code Coverage
+    steps:
+      - uses: actions/checkout@v4
+      # Nightly Rust is used for cargo llvm-cov --doc below.
+      - uses: dtolnay/rust-toolchain@nightly
+        with:
+          components: llvm-tools-preview
+      - name: Install cargo-llvm-cov
+        uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-llvm-cov
+      - name: Meilisearch (latest version) setup with Docker
+        run: docker run -d -p 7700:7700 getmeili/meilisearch:latest meilisearch --no-analytics --master-key=masterKey
+      - name: Collect coverage data
+        # Generate separate reports for tests and doctests, and combine them.
+        run: |
+          cargo llvm-cov --no-report --all-features --workspace
+          cargo llvm-cov --no-report --doc --all-features --workspace
+          cargo llvm-cov report --doctests --codecov --output-path codecov.json
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+          files: codecov.json
+          fail_ci_if_error: true