Give an option to reuse the anonymus user id between user changes instead of creating a new anonId every time

[Legion2]

Problem Statement

This is a copy of the issue from android: PostHog/posthog-android#224

Solution Brainstorm

See PostHog/posthog-android#224 for how it is implemented in android

[ioannisj]

@marandaneto I see that Android opted for a config option. A flag on reset() may have been more flexible approach though?

[marandaneto]

@marandaneto I see that Android opted for a config option. A flag on reset() may have been more flexible approach though?

see the linked PR, there's some comments/context on why just reset wouldn't work

[ioannisj]

Ah right I see now. Config options seems simpler in that case