## Because
- `fxa-admin-panel` was the last React package on `react-scripts` and `@rescripts/cli`. The rest of the monorepo builds with webpack 5.
- `@rescripts/cli` is unmaintained. It held the panel on an old toolchain, and the build needed `--openssl-legacy-provider` and `SKIP_PREFLIGHT_CHECK` to run at all.
- `react-scripts` also pinned Jest to 27, below the peer range of `ts-jest ^29.2.3`.
## This pull request
- Adds `config/webpack.config.js` and `config/webpackDevServer.config.js`, and points `build-react` and the new `start-react` script at them.
- Adds `jest.config.js`. It derives the same `moduleNameMapper` from the `tsconfig.base.json` paths that the rescripts config used.
- Deletes `.rescriptsrc.js` and `packages/fxa-react/configs/rescripts.js`, and drops the `./configs/rescripts` export from `fxa-react`.
- Updates `pm2.config.js` for the new dev server. Declares the SVG and CSS modules in `src/react-app-env.d.ts` that the `react-scripts` types used to cover.
- Bumps `jest` to `^29.7.0` and adds `jest-environment-jsdom ^29.7.0`. Jest 28 dropped the bundled jsdom environment, and `jest.config.js` asks for `testEnvironment: 'jsdom'`.
## Issue that this pull request solves
Closes: https://mozilla-hub.atlassian.net/browse/FXA-11853