Add more Cursor rules files about SDK topics

### Description

We have an [overview file](https://github.com/getsentry/sentry-java/blob/main/.cursor/rules/overview_dev.mdc) for Cursor (and other AI).

It's a sort of index file that's always applied to Cursors context. Cursor should then load more detailed rules files mentioned in the overview file based on your prompt.

The intent is to have AI be as helpful as possible while occupying minimal tokens by only loading what's needed.

For the future I was planning on adding more rules files as we go and touch certain areas of the SDK / implement new features. If there's specific rules files you think would help you, please comment here.