Make deployable on IPFS

[glamperd]

We should have an instance of the final version code deployed on IPFS such that this is a viable option for many users to run the front end. The aim is to have a content-addressed link for the sake of transparency wrt the code that users are running.

[glamperd]

IPFS deployment will require some variations to the code:

• routes need to be specified using # prefixes in the URL. HashRouter achieves this.
• The redirect that happens after sign-in can no longer be a static URL.
• The query parameters transferred in that same call must follow the #
• COOP/COEP headers must be provided by the IPFS gateway. The go-ipfs configuration allows this.

[glamperd]

TODO:

• [x] Check _redirects. Does it provide a better way to handle the signin redirect?
• [x] Need publicly available IP address on server.
• [x] Conditional compile: An option to npm run build-ipfs
• [x] Notes on how to build the IPFS deployment
• [ ] Docker deployment script ??
• [x] Merge main branch updates

[glamperd]

COOP/COEP headers can be done using a service worker. No need now for a customised IPFS gateway.

[glamperd]

Conditional compile is no longer necessary. The service worker is useful for other purposes. We'll revert to having a single build option.

The redirect URL will be determined from the URL at runtime even when running from a server. It will still be possible to override the redirect by adding a REACT_APP_SIGNIN_REDIRECT_URL environment var.

The sequencer URL will need to be specified in .env to build for IPFS