tsconfig.json: don't typecheck esbuild plugins

Our TypeScript config is setup to check our code that will be bundled
and run in the browser.  It shouldn't be running on esbuild plugins
that are run inside of node, and we never intended for it to.
Unfortunately, we mix our esbuild plugins into pkg/lib/ alongside
browser-based code, so it gets lumped in.

Add some excludes.  Fortunately, we don't have to copy this to other
projects (like Cockpit Files) because they only check `src/*` in the
first place (and only include files in other directories if they are
explicitly imported).

tsconfig.json

@@ -28,4 +28,10 @@
     "include": [
         "pkg/**/*"
     ],
+    "exclude": [
+        // these are part of the build system, not the app
+        "pkg/lib/esbuild-*.js",
+        "pkg/lib/cockpit-*-plugin.js",
+        "pkg/lib/*2po.js"
+    ],
 }