[Feature]: Create handler for the Set Contract Admin proposal type

[triccs]

Summary

This would allow users to submit a proposal of the type "set contract admin" which is important specifically so that Membrane can ask Osmosis Governance to migrate its governance contract admin ala Prop 695.

Current situation:

Problem Definition

Users are unable to use a proposal type defined by Osmosis and within the CLI. This would solve Membrane's problems described in Prop 695. As a budding Cosmwasm execution environment this is the first but may not be the last use & its a way for Osmosis to use its abilities to aid aligned protocols through governance.

Proposed Feature

Create a handler for the proposal type, "set contract admin"