UX: Return epoch where fund/release happened

[adlrocha]

Returning the epoch where a fund or a release happened can be really helpful to improve the UX of cross-net messages. That way users can have a sense of the next checkpoint in which their cross-net message will be included, so they can monitor the commitment of checkpoints and know when to expect their message to be committed. This can also help us debug a lot.

Additionally, this may become a requirement for the implementation of https://github.com/consensus-shipyard/ipc-agent/issues/151

[cryptoAtwill]

See #191