allow anonymous uuid generation to be customizable

[jimexist]

:bulb: Motivation and Context

this makes it aligned with the js/ts sdk

• https://github.com/PostHog/posthog-js/blob/55694356e168568700f3370f26d636cbe09bf795/src/posthog-core.ts#L169
• https://github.com/PostHog/posthog-ios/pull/133

:green_heart: How did you test it?

unit test

:pencil: Checklist

• [ ] I reviewed the submitted code.
• [ ] I added tests to verify the changes.
• [ ] I updated the docs if needed.
• [ ] No breaking change or entry added to the changelog.

[marandaneto]

@jimexist thanks for the PR. I left 2 more comments, please add a https://github.com/PostHog/posthog-android/blob/main/CHANGELOG.md#next entry under the Next section.

[marandaneto]

@jimexist run make api and commit/push the changes, I tried to do it myself but jimexist/main (permission denied).