doc: Move Thingy:91 and Thingy:91 x under application development

[divipillai]

Moved Thingy:91 and Thingy:91 x under application development.

NCSDK-29643

[NordicBuilder]

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Build number: 9

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Enabled	Name	Description
	ci-disabled	Disable the ci execution
	ci-all-test	Run all of ci, no test spec filtering will be done
	ci-force-downstream	Force execution of downstream even if twister fails
	ci-run-twister	Force run twister
	ci-run-zephyr-twister	Force run zephyr twister

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• ◻️ Build twister
• ◻️ Integration tests

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