Manually start and stop session recordings

[ioannisj]

Description

Ticket: https://posthoghelp.zendesk.com/agent/tickets/20809

Add APIs to allow for manual start/stop of session recordings

• iOS
• Android
• RN
• Flutter

https://github.com/PostHog/posthog-js/blob/1b57ea9f6b7736f3e3fce0fd512b467ddb35c5d9/src/posthog-core.ts#L1837

This option is an alternative for:

• Sampling
• Minimal duration
• Screen by screen basis

[marandaneto]

@ioannisj Android and RN as well, you can add the checklist and associate with the GH projects

[marandaneto]

A workaround for this is to call optOut() when you want to stop recording and optIn() when you want to resume recording, the only problem is that this also stops events from being captured (prod. analytics), so ideally we'd add a new method to start/stop session recording.