Adding a CI (also for deploying the SC)

[nielstron]

I currently see two options for this

• we supply secret keys with access to preview Ogmios instances on demeter.run and funds on preview testnet, then run the script in the CI
  • pro: small effort
  • pro: actually reflects whats happening on preview testnet
  • con: nondeterministic, depends on a contract address loaded with funds, the network up and running
• we launch a small node testnet, spin up ogmios etc
  • pro: deterministic and independent of whats happening on the preview testnet
  • con: large effort

Would help catch issues such as #1 quickly