refactor: add web-ext dependency and use it in the lint check

This commit makes the lint pipeline run web-ext from this repo's
package.json dependency, which will be cached in pnpm's store and thus
be installed quicker than if it was installed standalone.

Bug: twpowertools:212
Change-Id: I6da60ac9b858b8298cbc992ebf208da1d5b00094
diff --git a/package.json b/package.json
index 4630194..3223a1b 100644
--- a/package.json
+++ b/package.json
@@ -50,6 +50,7 @@
     "ts-node": "10.9.2",
     "typescript": "5.4.5",
     "typescript-eslint": "8.0.0-alpha.24",
+    "web-ext": "^8.0.0",
     "webpack": "5.91.0",
     "webpack-cli": "5.1.4",
     "webpack-preprocessor-loader": "1.3.0",