ci: add skip directives for long tests (#3151)

This PR introduces many CI optimizations:

1. The `[ci-skip]` PR body directive to skip the Postgres and end to end tests
2. Improved caching that cuts the Go test matrix in half
3. Increasing Go test parallelism for ~20% gains
4. Enable caching in webpack (4x frontend build)

site/webpack.common.ts

@@ -93,6 +93,10 @@ export const createCommonWebpackConfig = (options?: { skipTypecheck: boolean }):
     ],
   },
 
+  cache: {
+    type: "filesystem",
+  },
+
   // resolve extend/modify how modules are resolved.
   //
   // REMARK: Do not add aliases here, unless they cannot be defined in a