Add "/server-info/" frontend endpoint in development builds

[waxlamp]

This PR adds an "endpoint" to the frontend that proxies to the backend server info endpoint, emulating the mechanism in place on the Netlify-controlled deploys.

This works but only if you ask for the path complete with trailing slash, and I'm not sure why. Reviewers, perhaps you can recommend a better way to make this work so that the trailing slash is not required.

Closes #1108.

[danlamanna]

I think a better solution would be to proxy /api, making it a standard that a $gui_url/api is the location for retrieving information.

[waxlamp]

I think a better solution would be to proxy /api, making it a standard that a $gui_url/api is the location for retrieving information.

I agree, and I'll file an issue to make this the standard way the API is proxied through to the front end, but if we can merge this PR, it will provide the CLI team immediate value, and then we can get to the fuller solution afterwards.

[yarikoptic]

confirming that it works as intended:

$> curl http://localhost:8085/server-info/
{"schema_version":"0.6.3","schema_url":"https://raw.githubusercontent.com/dandi/schema/master/releases/0.6.3/dandiset.json","version":"0.2.39.post19+g9b92512f","services":{"api":{"url":"http://localhost:8000/api"},"webui":{"url":"http://localhost:8085"},"jupyterhub":{"url":"https://hub.dandiarchive.org/"}},"cli-minimal-version":"0.14.2","cli-bad-versions":[]}

(whenever on master it gives html page about JS needed etc).

[dandibot]

🚀 PR was released in v0.2.42 🚀