Default maximum size of an HTTP request to be proxied is now 100MiB (was
1MiB), and is a setting that can be viewed in the UI and set and run time
via the `GATEWAY_MAX_REQUEST_SIZE` environment variable.

Run linting via pre-commit hook (or manually).

Update version of Auto-DevOps used in CI.

Add an authentication token to proxied requests which mirrors the
authentication token passed to backends by the "real" gateway.

Closes #2