ci: add caching for Go modules and Maven dependencies

Add caching to speed up CI builds by caching:
- Go modules (~/.cache/go-build and ~/go/pkg/mod) based on go.sum
- Maven dependencies (~/.m2/repository) based on pom.xml

This significantly reduces build times by avoiding re-downloading
dependencies on every CI run. Cache keys are based on dependency
file hashes, so cache is invalidated when dependencies change.

Benefits:
- Faster Go builds (no need to download modules each time)
- Faster Maven builds (no need to download dependencies each time)
- Reduced network usage and CI minutes

Author: casibbald

.github/workflows/tilt-ci.yaml

@@ -46,6 +46,16 @@ jobs:
           go-version: '1.23'
           check-latest: true
 
+      - name: Cache Go modules
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/go-build
+            ~/go/pkg/mod
+          key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+          restore-keys: |
+            ${{ runner.os }}-go-
+
       - name: Setup Helm
         uses: azure/setup-helm@v4
         with:
@@ -257,6 +267,14 @@ jobs:
           java -version
           mvn --version
 
+      - name: Cache Maven dependencies
+        uses: actions/cache@v4
+        with:
+          path: ~/.m2/repository
+          key: ${{ runner.os }}-maven-${{ hashFiles('demo-app/pom.xml') }}
+          restore-keys: |
+            ${{ runner.os }}-maven-
+
       - name: Get dependencies
         run: go mod download