Add Governor module for governance-settable parameters

[Amxx]

Fixes #2903
Fixes #2866

PR Checklist

• Tests
• Documentation
• Changelog entry

[Amxx]

Note: this PR does change the governor's interfaceId

[frangio]

Note: this PR does change the governor's interfaceId

This doesn't sound good... The interface id is already being depended on, I don't think we can change it.

[Amxx]

Whould that be good ?

    function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC165) returns (bool) {
        // In addition to the current interfaceId, also support previous version of the interfaceId that did not
        // include the proposalThreshold() function as standard
        return interfaceId == (type(IGovernor).interfaceId ^ this.proposalThreshold.selector)
            || interfaceId == type(IGovernor).interfaceId
            || super.supportsInterface(interfaceId);
    }

[apbendi]

hey @Amxx, just curious about the state of this PR and when we might expect it to land. Thanks!

[Amxx]

Soon :)

[frangio]

@apbendi To be a little more specific this will land in 4.4, which will have a release candidate out in the next several days. The final release will come a few weeks later than that.