Add README badge with libyear count

The above is done with the help of a new pipeline step. It uses libyear to calculate how outdated each dependency (including indirect) is.
Then, it uses a Github Action called "Bring Your Own Badge". This action commits the count made by libyear to a "shields" branch. This is count is later referenced in the project's README.

Signed-off-by: João Henri <joao.henri.cr@gmail.com>

.github/workflows/ci.yaml

@@ -319,7 +319,7 @@ jobs:
           kind get kubeconfig > $HOME/.kube/kind-config-kind
           make kind-e2e-test
 
-      - name: Uplaod e2e junit-reports
+      - name: Upload e2e junit-reports
         uses: actions/upload-artifact@83fd05a356d7e2593de66fc9913b3002723633cb # v3.1.1
         if: success() || failure()
         with:
@@ -374,7 +374,7 @@ jobs:
           kind get kubeconfig > $HOME/.kube/kind-config-kind
           make kind-e2e-test
 
-      - name: Uplaod e2e junit-reports
+      - name: Upload e2e junit-reports
         uses: actions/upload-artifact@83fd05a356d7e2593de66fc9913b3002723633cb # v3.1.1
         if: success() || failure()
         with:
@@ -492,3 +492,38 @@ jobs:
         if: ${{ steps.filter-images.outputs.kube-webhook-certgen == 'true' }}
         run: |
           cd images/kube-webhook-certgen && make test test-e2e
+
+  libyear:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write  # for RubbaBoy/BYOB to write to "shields" branch
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@755da8c3cf115ac066823e79a1e1788f8940201b # v3.2.0
+
+      - name: Set up Go
+        id: go
+        uses: actions/setup-go@6edd4406fa81c3da01a34fa6f6343087c207a568 # v3.5.0
+        with:
+          go-version: '1.19'
+          check-latest: true
+
+      - name: Install libyear
+        run: go install git.yetaga.in/alazyreader/libyear@latest
+
+      - name: Run libyear
+        id: libyear
+        run: |
+          LIBYEAR_COUNT=$(libyear -indirect | tail -1 | sed -e "s/total libyear count: //")
+          echo "LIBYEAR_COUNT=${LIBYEAR_COUNT}" >> $GITHUB_OUTPUT
+
+      - name: Update Libyear badge
+        uses: RubbaBoy/BYOB@v1.3.0
+        with:
+          NAME: libyear
+          COLOR: blue
+          LABEL: 'libyear count'
+          STATUS: ${{ steps.libyear.outputs.LIBYEAR_COUNT }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}