docs: show live examples in favor of static images

[ndonkoHenri]

• examples-gallery Flet app is a simple app which contains routes to each control's examples.
• It gets packaged (by flet publish) at docs runtime, and is hosted along with the docs at /apps/examples-gallery/dist/
• in each control documentation, a macro is used to embed the corresponding live-example as an iframe.
• corresponding images have been removed in favour of the live demo.

Notes:

• [ ] WebView - flet.dev refused to connect.
• [ ] Video - shows blue screen
• [ ] VerticalDivider - Adjust size, it's too small on desktop
• [ ] TransparentPointer - Maybe display Text on the page instead of prints?
• [ ] TimePicker - basic example doesn't open TimePicker
• [ ] TextField:
  • basic example: heigh of frame is too short and it's impossible to click on Submit button
  • handling change events: Text is not displayed on the screen (maybe page.update() doesn't work?)
  • handling selection changes: buttons don't work
  • multiline fields: if you enter more rows then TextFields don't fit, maybe scrolling is needed for the page.
  • setting prefixes and suffixes: Submit button doesn't work
• [ ] TextButton: handling clicks - on_click doesn't work
• [ ] In general, events that update controls don't work