chore(issue templates): small tweaks + clear mention of support window (#35304)

Summary:
During the outage it become clear that we are not doing enough to communicate what the release support policy/window is. This is one of the tweaks I'm doing to help with that

## Changelog

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[Internal] [Changed] - small tweaks to issue templates + clear mention of support window

Pull Request resolved: https://github.com/facebook/react-native/pull/35304

Test Plan: N/A

Reviewed By: christophpurrer

Differential Revision: D41183435

Pulled By: cipolleschi

fbshipit-source-id: 32519c52616fb1903507fad291200eb959d451b4