Update Gateway conditions `LastTransitionTime` only when needed

[mlavacca]

Problem Statement

Every time The Gateway status gets updated because of a condition change, all the conditions look like they transitioned, as the LastTransitionTime gets updated for all of them.

When a condition changes or gets added, all the other Gateway conditions LastTransitionTime fields shouldn't get updated.

Acceptance Criteria

• The LastTransitionTime field of the Gateway condition doesn't change when the condition doesn't actually get updated.
• The above condition is ensured in an integration test

[github-actions]

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