feat: banner UI/UX adjustments (#5151)

https://linear.app/unleash/issue/2-1549/ui-align-with-uiux

Includes UI/UX adjustments to the banners feature after aligning with
@nicolaesocaciu

There are a lot of changes, but here are a few:
 - Redesigned preview section
 - Redesigned banner status (enabled) section
 - Reordered form fields to better fit the flow
 - Reordered fields in the side-panel payload to reflect order in the UI
 - Made inputs full width
 - Adjusted multiline fields
 - Added a link to Markdown's basic syntax examples
 - Added a "preview dialog" button
 - Updated `HelpIcon` usage to use the `htmlTooltip`
- Improved `Banner` inline design, added a maxHeight prop for usage
inside a table
 - Improved `FormSwitch` design


![image](https://github.com/Unleash/unleash/assets/14320932/d8fe1f59-85ed-48eb-aa46-62628b12f0b1)

Co-authored-by: Nicolae <[email protected]>