chore: Removed NStack feature integration

[utpal-barman]

General

Important

Notes regarding NStack

NStack might currently be down as the organization plans to sunset this service.
However, this guide will assist future developers if they choose to work with it &
NStack is up again. We are removing this feature from the Flutter Template as
we decided internally.

• Jira Ticket

Checklists

• Platform specific changes (input, image picking etc) are tested on both of the platforms (Android and iOS)
• It is tested that the UI changes are rendered correctly on different device sizes (such as long lists or expanded rows) with safe area conditions.
• Edge cases, such as responses being empty or invalid, missing data, no internet connection etc, are tested and the app works as expected.

Showcase

• Either showcase screenshots / videos are attached, or this PR does not require such any showcase.

[nivisi]

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