feat: ✨ sd-input with sd-autocomplete loading indicator

[Fl0rianFischer]

User Story

As a user of the Solid Design System, I would like to be informed if a backend request is completing if I'm using the input as an async search field in combination with sd-autocomplete

Suggested Solution

• add a prop loading to sd-input
• replace search icon with loading indicator while loading prop is true

Subtasks

• [ ] Design_implementation_task
• [ ] Development_implementation_task
• [ ] Design_release_task

DoR

• [ ] Item has business value
• [ ] Item all subtasks have been estimated by the team
• [ ] Item is clear and well-defined
• [ ] Item dependencies have been identified

DoD

• [ ] All subtasks have been closed