Add method documentation for Posthog

[marandaneto]

Description

Relates to https://x.com/caseycrogers/status/1763498570307551663?s=20

[caseycrogers]

Motivating example:
I want to set when events are associated with a dev device so I can filter that out in my dashboards. debug(true) seems like the obvious thing to do, but when I click through on debug it's not documented so I'm not sure what setting it to true does.

Of course I can reference the web docs (which I'm about to do now to read up on this), but 9 times out of 10 I prefer in-line documentation as it's much less disruptive to my workflow than having to navigate web docs.

[marandaneto]

We'd also benefit from automatically generated API ref. https://pub.dev/documentation/posthog_flutter/latest/index.html

[dreyescabrera]

How can I assist with this? I believe it would be a great benefit to the community, me included.

[marandaneto]

How can I assist with this? I believe it would be a great benefit to the community, me included.

you pretty much copy the code comments from the Android SDK
And follow the Dart comments spec so the documentation will be automatically generated during the publish steps.