[Feature] Greatly improved forms with dbt profile browsing

[gwenwindflower]

This PR greatly improves the forms that compose the TUI, based on feedback from the dbt Labs DX team.

• Now unified into one form with conditional visibility rather than multiple forms with conditional logic
  • This allows shift+tab and tab to back/forward through the entire thing
• Validated input to prevent entering blank values
• Default values where sensible so you can Just Hit Enter
• We fetch all the dbt profiles before the form runs, so you can browse them rather than trying to enter the name correctly, this will error early if there are parsing issues with the profiles rather than after you fill out the form