Establish a plan for removing v1- commands

It would be good to establish a concrete plan and timeline for removing `v1-` commands from cabal.

This has come up two years ago in #9109 and a year ago in #10262 but it's a very hard task to progress on without coming up with a proposal and overall plan.

**If we start from the premise that we want to remove the v1-commands eventually, how do we get there?**

I have made this ticket as I need something to track the task with but I'm planning to write down something more concrete and detailed about a possible way forward.

Start by reading the discussion in issues #9109 and #10262 to understand the prior concerns around removing v1-commands from cabal. Define a concrete proposal, migration steps, and timeline for eventual removal; the issue is complete when that plan is documented and actionable.

Written by the indexing model from the issue text.