feat: Migration tool for agents pre DB refactor (pre 0.2.12)

[cpacker]

Please describe the purpose of this pull request.

• Add migration tool that automatically converts old agent folders into the new format
• Make migration UX nice
  • on the first run of the new refactor release, users should see a prompt asking them if they want to migrate old agents
  • for the initial release past the refactor, should also add a "Don't see old agents? Make sure you run the migration command" hint to the agent selection screen

How to test

• Try migrating old agent folders, manually inspect the new data to make sure it matches

Have you tested this PR?

WIP

Related issues or PRs

#708

[cpacker]

Redoing in #802