Check if Certora Key is set in the repo for CI (#52)

This PR adds a check to see if the `CERTORA_KEY` is set or not to run
the CI. If the key is not set, the Certora check will show as "Skipped"
instead of Success in the GitHub Actions.

This ensures that the repo can be upstreamed to Candide without any
immediate failure to the CI. It also ensures that it doesn't show the
impression of FV passing without verification.

P.S. I have disabled the ruleset which required all the FV tasks to be
successful so this could be included.

.github/workflows/certora_recovery.yml

@@ -8,8 +8,30 @@ on:
     branches:
       - main
 
+env:
+  CERTORAKEY: ${{ secrets.CERTORA_KEY }}
+
 jobs:
+  check-secret:
+    runs-on: ubuntu-latest
+    outputs:
+      certora-key-exists: ${{ steps.certora-key-check.outputs.defined }}
+    steps:
+      - name: Check for Certora Secret availability
+        id: certora-key-check
+        # perform secret check & put boolean result as an output
+        run: |
+          if [[ -n "${CERTORAKEY}" ]]; then
+            echo "defined=true" >> $GITHUB_OUTPUT;
+            echo "CERTORA_KEY exists"
+          else
+            echo "defined=false" >> $GITHUB_OUTPUT;
+            echo "CERTORA_KEY does not exist"
+          fi
+
   verify:
+    needs: [check-secret]
+    if: needs.check-secret.outputs.certora-key-exists == 'true'
     runs-on: ubuntu-latest
     strategy:
       matrix:
@@ -43,7 +65,4 @@ jobs:
 
       - name: Verify rule ${{ matrix.rule }}
         run: |
-          echo "Certora key length" ${#CERTORAKEY}
           certoraRun certora/conf/${{ matrix.rule }}.conf --wait_for_results=all
-        env:
-          CERTORAKEY: ${{ secrets.CERTORA_KEY }}