refactor: remove consumer to require gov authority on some operations

[julienrbrt]

Closes: #48

• RemoveConsumer now is authority-only (via gov)
• Restrict owner post-launch to metadata-only
• Add consumer chains events to allow building tooling for chain updates
• Add downtime grace period (after launch)

Launching the chain is fine, as you need 66% of the validators to be up to be marked as launched.

[giunatale]

I don't know we need to discuss what model are we exactly after here.

In a permissionless setting, the owner should be allowed to shutdown the consumer I guess. The way it's set up by this PR the only way to do that is to let the consumer run out of funds, or ask provider governance (which may have an incentive to let the consumer continue spending the funds left in the fee pool). And with #46 the owner can't sweep funds if the chain is launched, so they have to wait for funds to be depleted and can't recover them.

Not saying this is wrong necessarily, but I see some contradictory pulls between wanting a permissionless vs permissioned model.

[giunatale]

LGTM, pretty straightforward

Provided we clarified our divergences outside of this PR, so my earlier comment doesn't apply.