feat(user-manual): Add docs for mail snippets

[hamza221]

☑️ Resolves

• part of #10113

🖼️ Screenshots

[nimishavijay]

• [ ] Snippets --> Text blocks
• [ ] Move the section in the settings to below General

Inside setting dialog

• [ ] Snippets heading --> list of snippets --> Create new snippet button
• [ ] For each snippet use NcListItem component with title in one line and content in subline and 3 dot menu
• [ ] Add shared icon to the left of 3 dot menu
• [ ] In 3 dot menu delete at the end
• [ ] In 3 dot menu For edit use pencil icon
• [ ] Nice-to-have: show share icon if it's shared with other people

• [ ] new snippet dialog and edit snippet dialog --> add border in content so that it looks like a text field
  • [ ] Buttons in new and edit dialog
  • [ ] "Ok" --> "Save text block"
  • [ ] Cancel icon --> x symbol
  • [ ] Cancel button tertiary
  • [ ] width of the buttons should be fit-content
  • [ ] all buttons right aligned
• [ ] Edit dialog
  • [ ] width same as new snippet dialog
  • [ ] remove "Content" heading
  • [ ] "Shares" --> h3
  • [ ] Add placeholder in dropdown "Search for users or groups"
  • [ ] Instead of UserBubble component for added users use NcListItem (similar to calendar sharing or files sharing) with an x to remove

Incoming shared text blocks

• [ ] Allow opening and viewing full text block
• [ ] Hide section if empty

While inserting in composer

• [ ] character?
• [ ] in 3 dot menu have "Insert text block" item after smart picker item
• [ ] Open modal with list of text blocks and search bar which filters the results similar to Talk create conversation add participants modal

Follow up

• [ ] combine with smart picker

[rakekniven]

Everything else looks good!