x/authz pruning and gas

[aaronc]

Following up from #7105 (comment), as improvements to the core x/authz implementations it would be desirable to:

• DONE support some method for pruning expired authorizations
• have a gas fee or some other financial mechanism to prevent lots of spurious authorizations from polluting state

[robert-zaremba]

Do we have any framework, guidelines or simulation about gas costs?

[robert-zaremba]

My proposal for storage is following:

1. charge small amount of gas
2. and require a stake, which will be released once we delete the storage.

This is what Ethereum simulations and research are suggesting.

[clevinson]

Let's put this in the icebox until we have a better solution for deposits for messages like this.