Add a deployment workflow for the frontend

[dhess]

Now that we have a semi-functional frontend implementation in this repo, we should automatically deploy it on successful merges to main (and probably even for PRs). This should be relatively easy to do as it's entirely browser-based and can be distributed via CDN.

The easiest way to do this is by building the frontend during CI and storing it in Nix, then pushing that Nix artifact during the CD step (post-merge to main). Therefore, I'd like to wait for Wasm support in haskell.nix, assuming that merges in the not-too-distant future:

• Add support for WASM backend input-output-hk/haskell.nix#2351