test(integration): Add integration tests for Docker export to cache

- Add comprehensive integration tests for exportToCache functionality
- Test default behavior (no export)
- Test export via package config
- Test CLI flag override (both directions)
- Test environment variable
- Test metadata extraction from exported images
- Verify cache artifact structure and content

Co-authored-by: Ona <no-reply@ona.com>

Author: leodido

pkg/leeway/build.go

@@ -2167,7 +2167,6 @@ func createDockerExportMetadata(wd, version string, cfg DockerPkgConfig) error {
 	return nil
 }
 
-
 // Update buildGeneric to use compression arg helper
 func (p *Package) buildGeneric(buildctx *buildContext, wd, result string) (res *packageBuild, err error) {
 	cfg, ok := p.Config.(GenericPkgConfig)