fix: change healthcheck to query 127.0.0.1

See merge request !2

Add max HTTP request size setting and increase default

Closes #1

See merge request !1

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

Add a healthcheck command which enables docker compose configurations
using the gateway image to wait for the service to be healthy. This is
done mirroring the existing `wget` command used in our boilerplate.

Add a simple docker compose configuration which can be used to test the
application in local development.