feat: add edit model cli and tui

[sammcj]

• Feat: Add 'Edit Model'
  • BREAKING: 'Update Model' (u) has been replaced with 'Edit Model' (e)
  • This should reduce keybinding overload
  • It's a simpler but more reliable function
  • Can be called on the command line with gollama -e <model name>
• Docs: Add @fahdmirza's youtube video (Sorry that took a while, I thought I'd already done it!)