Make feature flags optional

[aayush-se]

This PR makes the feature_flags returned by the get_issue_filter_keys RPC optional.

Previously, feature flags were always fetched and included in the response. This change introduces an include_feature_flags: bool = True parameter, allowing callers to explicitly opt-out of fetching and receiving feature flags. This improves performance when feature flags are not needed.

[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
_{Learn more about Cursor Agents}

[getsantry]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you add the label WIP, I will leave it alone unless WIP is removed ... forever!

---

"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀