chore: add more test coverage for edge function tarball bundling

updating our existing edge function tests to run with both default (eszip2) and tarball
bundling configurations using feature flag variants

Author: JakeChampion

packages/build/src/core/feature_flags.ts

@@ -19,4 +19,5 @@ export const DEFAULT_FEATURE_FLAGS: FeatureFlags = {
   buildbot_zisi_esbuild_parser: false,
   netlify_build_updated_plugin_compatibility: false,
   netlify_build_plugin_system_log: false,
+  edge_bundler_generate_tarball: false,
 }