Nix Derivation/Shell for quick setup

[Benjmhart]

1. the existing ogmios derivation appears to be broken.
2. we need a quick way (modulo syncing) to get a testnet + chain index running - this may already exists, in which case just shoot the docs to @Benjmhart, can be nix, docker, etc.

this will facilitate cardano-browser-tx development while we add datum features

[Benjmhart]

[ngua]

I'm going to try to take care of this today by fixing the flake.nix

[ngua]

For the second item, @mikekeke has a gist for setting up the hosted PAB scenario which includes how to get the testnet and chain index running: https://gist.github.com/mikekeke/883d56c38e0237444ac98ae5257e174f#gistcomment-3962799

[zygomeb]

closed by #2