feat: add downloadBaseURL and checksum inputs (closes #206)

.github/workflows/integration-tests.yml

@@ -54,3 +54,32 @@ jobs:
 
          - name: Validate kubectl setup old version
            run: python test/validate-kubectl.py 'v1.15.1'
+
+         - name: Fetch known SHA256 for v1.30.0 linux/amd64
+           id: sha
+           run: |
+              value=$(curl -fsSL https://dl.k8s.io/release/v1.30.0/bin/linux/amd64/kubectl.sha256)
+              echo "value=$value" >> "$GITHUB_OUTPUT"
+
+         - name: Setup kubectl with valid checksum
+           uses: ./
+           with:
+              version: 'v1.30.0'
+              checksum: ${{ steps.sha.outputs.value }}
+
+         - name: Validate kubectl setup with checksum
+           run: python test/validate-kubectl.py 'v1.30.0'
+
+         - name: Setup kubectl with bad checksum (expect failure)
+           id: badsum
+           continue-on-error: true
+           uses: ./
+           with:
+              version: 'v1.29.0'
+              checksum: 'deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef'
+
+         - name: Assert bad-checksum step failed
+           if: steps.badsum.outcome != 'failure'
+           run: |
+              echo "Expected bad-checksum step to fail, but outcome was: ${{ steps.badsum.outcome }}"
+              exit 1