fix(content-server): Add explicit webpack alias for @fxa/shared/sentry-utils

Because:
- Even with TsconfigPathsPlugin configured against tsconfig.base.json,
  webpack in content-server was emitting webpackMissingModule for
  @fxa/shared/sentry-utils — the one new path import from app-side code
  (app/scripts/lib/sentry.js). This surfaced as a pageError at runtime
  ("Cannot find module '@fxa/shared/sentry-utils'") and broke the
  app.bundle.js initialization path, causing the cookiesDisabled
  Playwright test to hang waiting for the redirect to /cookies_disabled.

This commit:
- Adds a direct resolve.alias entry for @fxa/shared/sentry-utils pointing
  at libs/shared/sentry-utils/src/index.ts, mirroring the existing
  @fxa/vendored aliases.

Author: dschom

packages/fxa-content-server/webpack.config.js

@@ -96,6 +96,10 @@ const webpackConfig = {
         __dirname,
         '../../libs/vendored/incremental-encoder/src/index.ts'
       ),
+      '@fxa/shared/sentry-utils': path.resolve(
+        __dirname,
+        '../../libs/shared/sentry-utils/src/index.ts'
+      ),
     },
   },