add event notification to covenant contracts

[bekauz]

Currently it's a little tedious to track the state machine progress of all covenants.

Lets try to introduce an event notification system that would help deal with this:

• upon advancing the state of any covenant-instantiated contract, the contract submits a message to its admin (=covenant) that includes a timestamp and description of what happened
• covenant validates the sender of msg to be one of its instantiated contracts
• covenant stores the events in a sorted ds (BTreeSet?) and exposes it via query

Logic for this is generic enough to sit in covenant_utils.

Things to consider:

• query the covenant address on-demand via query_wasm_contract_info(env.contract.address)?.creator or store the admin address in storage
• use a specific event structure or just the cw_utils::Event
• is it worth to paginate the query (as the swap covenant may be like 5 events in the happy case)
• how much do we want to notify of? bare minimum or fully lean into event sourcing?

[uditvira]

I really like this. However, I'd like to prioritize getting the two-party functionality and Osmosis integration complete before we work on quality of life improvements for users