feat: session id support for payloads

[EDsCODE]

What does this PR do?

Where should the reviewer start?

How should this be manually tested?

Any background context you want to provide?

What are the relevant tickets?

Screenshots or screencasts (if UI/UX change)

Questions:

• Does the docs need an update?
• Are there any security concerns?
• Do we need to update engineering / success?

[liyiy]

I think we're also missing a resetSessionId method ?

[neilkakkar]

Adding Ben just for sess-rec awareness

[benjackwhite]

Happy to add a review but not sure it has much impact on sesh-rec world...?

[neilkakkar]

D'oh, right, you wouldn't need this at all, since no session recordings on mobile 🤦

[marandaneto]

Closed in favor of https://github.com/PostHog/posthog-ios/pull/100