Fix for #348 - migrate our NextJS project to a pure webpack project w/ a single bundle

• Switch from next/link to react-router-dom's link

This part was easy - just change the import to import { Link } from "react-router-dom" and <Link href={...} /> to <Link to={...} />

• Switch from next/router to react-router-dom's paradigms (useNavigation, useLocation, and useParams)

router.push can be converted to navigate(...) (provided by the useNavigate hook)
router.replace can be converted navigate(..., {replace: true})
Query parameters (const { query } = useRouter) can be converted to const query = useParams())

• Implement client-side routing with react-router-dom

Parameterized routes in NextJS like projects/[organization]/[project] would look like:

              <Route path="projects">
                   <Route path=":organization/:project">
                   <Route index element={<ProjectPage />} />
                 </Route>
              </Route>

• Bring back webpack-* dependencies and remove next dependencies
• Get unit tests green
• Migrate webpack.config.ts
• Fix up package.json commands (dev vs production)
• Remove nextrouter package, use simpler routing strategy
• Implement content-addressable bundle (proper caching behavior)
• Implement always-fallback to index.html
• ❌ Use child component instead of element

Found that this doesn't work with react-router-v6. Put on agenda for FE variety: https://www.notion.so/coderhq/2022-03-11-0154cfb8646348568443048bc3d2c970#15fe7476fb214da394bed746dcbbfd1e

• Implement 404 page
• Move html templates to html_templates folder
• Use Main.tsx as entry point
• Migrate _document.tsx to a static solution
• Bundle static icons (favicons, etc)
• Verify that login redirect parameters work correctly
• Verify cache headers
• Ensure injectable template parameters (ie, CSP nonces) get populated correctly
• Verify production build is produced correctly (minified, etc)
• Run webpack-bundle-analyzer to check bundle is correct
• Implement hot-reload via webpack-dev-server
• Clean up package.json dependencies
• Fix lint issues
• Fix go tests
• Port over webpack config comments
• Can the v1 embed strategy be used? If so, safer to use that than roll a new implementation 🤔
• Fix warnings in startup logs
• Merge fix: Update routes for project page, workspace creation page, and workspace page #415
• Fix E2E failure

I've hooked up a build:analyze command that spins up a server to show the bundle size:

The bundle looks OK, but there are some opportunities for improvement - the heavy-weight dependencies, like React, ReactDOM, Material-UI, and lodash could be brought in via a CDN: https://stackoverflow.com/questions/50645796/how-to-import-reactjs-material-ui-using-a-cdn-through-webpacks-externals

I'll defer this to a separate issue, but once those are extracted - the bundle should be fast and lean. Using the CDN for those dependencies is great for performance, because usually users will already have the libraries cached, and they are downloaded in parallel to our bundle.