feat(discover): add endpoint for single saved query updates

[lzhao-sentry]

Changes

Address part of EXP-1166 in effort to port the remaining discover queries to explore all queries. This PR adds:

• Discover starred endpoint to update starred status. API is not public yet

[linear-code]

EXP-1166

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

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[nikkikapadia]

lgtm just some comments on cursor's comments

[sentry]

Bug: The position field is accepted by the StarQuerySerializer but is silently ignored by the endpoint, which always appends the starred query to the end.
_{Severity: MEDIUM}

Suggested Fix

Modify the endpoint to read the position value from the validated serializer data. Update DiscoverSavedQueryStarredManager.insert_starred_query to accept an optional position parameter. If a position is provided, use it to insert the starred query at the specified location instead of always appending it.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: src/sentry/discover/endpoints/discover_saved_query_starred.py#L66-L70

Potential issue: The `StarQuerySerializer` accepts an optional `position` field, but the
endpoint logic silently ignores it. The code only reads the `is_starred` value from the
validated serializer data and never extracts or uses the `position`. The call to
`DiscoverSavedQueryStarredManager.insert_starred_query` does not pass a position;
instead, the underlying method always calculates a new position by calling
`next_starred_position`. This results in any client-provided `position` being
disregarded, and the starred query is always appended to the end of the list, leading to
unexpected ordering behavior.

[lzhao-sentry]

Not an issue because clients arent ordering the queries on creation, it's done automatically by insert_starred_query