ci(build): Build container image with local sources

Adds the build args to use the local sources when building the container
image. This is only for testing if the PowerAPI package can be installed
and the container image built.

Author: gfieni

.github/workflows/build.yml

@@ -64,3 +64,5 @@ jobs:
           provenance: false
           load: true
           tags: localbuild/powerapi:sha-${{ github.sha }}
+          build-args: |
+            POWERAPI_INSTALL_METHOD=local