feat(docs): Sandbox -> testnet guides + "try testnet" collation page #36836

Job	Run time
configure	0s
base-images	0s
ci-noir-bb	0s
bb-native-tests	0s
bootstrap	0s
acir-bench	0s
bb-bench	0s
ci-rest	0s
images-e2e	0s
docs	0s
boxes-test	0s
prover-client-test	0s
protocol-circuits-gates-report	0s
e2e	0s
public-functions-size-report	0s
kind-network-smoke	0s
bench-e2e	0s
e2e-prover-full	0s
kind-network-test	0s
merge-check	1s
notify	0s
	1s

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