FM-17: Map events to ABCI

[aakoshh]

Closes consensus-shipyard/ipc#286

Now that a new version of fvm_shared made the necessary fields public, was able to finish mapping events.

I think the Go version of EventAttribute might accept bytes, which it turns into Base64 strings during serialization; the Rust library expects String for key and value, which it will encode as Base64. The value coming from StampedEvent is Vec<u8>, so I first converted it hex, which then will be converted into Base64, which is a bit ugly, but not sure what else I could do (apart from double Base64 encoding, which could be shorter, but perhaps we use hex more often).

Here are some relevant docs:

• https://docs.cosmos.network/v0.46/core/events.html
• https://docs.tendermint.com/v0.34/tendermint-core/subscription.html
• https://docs.tendermint.com/v0.34/app-dev/indexing-transactions.html
• https://docs.ethermint.zone/quickstart/events.html