fix: update Java examples in the API Reference docs for Events and Subscribers Endpoints

[m-a-r-1912]

For this issue: 295
This draft PR is to show the progress of updating the API Reference docs for Java.
The Events methods have been updated and I'll continue to add more updated docs.

[unicodeveloper]

Hello @m-a-r-1912 Please do you have any update for this? It has been in draft mode for a week now

[m-a-r-1912]

Yes! I'll add my updates today.

[unicodeveloper]

Thanks for adding the updates. Are there other updates you want to add this current PR? If not, can you remove it from DRAFT? @m-a-r-1912

[m-a-r-1912]

The Java example changes for the Events and Subscribers endpoints should be good to review now. I didn't update all of the Subscribers Java examples because either the SDK method seemed to cause errors with the Novu API or there isn't an equivalent SDK method for the endpoint.
Edit: Also, there's several more sections of the API Reference docs that have out of date Java examples, but those can be updated with a different PR. Updating those would keep this PR open probably for too long