Releases: fix snapshot action in pre-release mode, create single tag per version instead of per package

[alvrs]

Some rough edges around the new changesets based release pipeline we should smooth out:

• it seems like the snapshot action fails on main now that main entered pre-release mode. Maybe we could have a step in the snapshot action to "exit" pre-release mode (without actually committing that change) to work around this?
• changesets creates an individual tag for each package+version, instead of a single tag per version. I think a single tag per version would be cleaner, since all versions are synced
• it would be nice if we had a global changelog like before with lerna (see [proposal] Aggregated/"monorepo" changelog in root of monorepo? changesets/changesets#264)

[alvrs]

Added an issue to changesets for the first point: changesets/changesets#1195. Will attempt to work around for now by exiting the pre-release mode in the action before releasing the snapshot release.

[alvrs]

fixed by #1256 and #1203