feat: add channel info screen to the sample app (#3499)

This pull request refactors the group member management UI in the sample
app by replacing the old single-member add bottom sheet with a new, more
modern multi-member add experience, and introduces a new bottom sheet
for viewing all members. The changes also remove the legacy
`AddMemberBottomSheet` and the custom animated overlay logic, in favor
of new, more maintainable components.

**Major UI Refactorings:**

* Added `AddMembersBottomSheet`, a new component allowing users to
search for and select multiple users to add to a channel at once, with a
modern, themed UI and improved user experience.
(`examples/SampleApp/src/components/AddMembersBottomSheet.tsx`)
* Added `AllMembersBottomSheet`, a new component for displaying all
channel members in a bottom sheet, with support for viewing member
details and adding new members.
(`examples/SampleApp/src/components/AllMembersBottomSheet.tsx`)

**Removals and Cleanups:**

* Removed the legacy `AddMemberBottomSheet` component, which only
supported adding one member at a time and used custom overlay logic.
(`examples/SampleApp/src/components/AddMemberBottomSheet.tsx`)
* Removed the custom `BottomSheetOverlay` component and its associated
gesture and animation logic, as the new bottom sheets use the built-in
modal system from `stream-chat-react-native`.
(`examples/SampleApp/src/components/BottomSheetOverlay.tsx`)

Author: khushal87