fix: add request body schema in update segment endpoint (#8085)

https://linear.app/unleash/issue/2-2592/updateimprove-a-segment-via-api-call

Related to #7987

This does not make the endpoint necessarily better - It's still a PUT
that acts as a PUT in some ways (expects specific required fields to be
present, resets the project to `null` if it's not included in the body)
and a PATCH in others (ignores most fields if they're not included in
the body). We need to have a more in-depth discussion about developing
long-term strategies for our API and respective OpenAPI spec.

However this at least includes the proper schema for the request body,
which is slightly better than before.

src/lib/features/segment/segment-controller.ts

@@ -195,9 +195,10 @@ export class SegmentsController extends Controller {
                 openApiService.validPath({
                     summary: 'Update segment by id',
                     description:
-                        'Updates the content of the segment with the provided payload. Any fields not specified will be left untouched.',
+                        'Updates the content of the segment with the provided payload. Requires `name` and `constraints` to be present. If `project` is not present, it will be set to `null`. Any other fields not specified will be left untouched.',
                     tags: ['Segments'],
                     operationId: 'updateSegment',
+                    requestBody: createRequestSchema('upsertSegmentSchema'),
                     responses: {
                         204: emptyResponse,
                         ...getStandardResponses(400, 401, 403, 409, 415),