[Issue Stream] Add runtime context to group details

In PR https://github.com/getsentry/sentry/pull/88312, runtime labels for JS Errors were added. Those "Frontend" and "Backend" labels should also be added to issue stream items like this (only JS SDK issues):


In the event details, this runtime context information is retrieved from the already existing event details. In the issue stream, this runtime information is not available, as the backend returns grouped issues.

Develop Docs: [Runtime Context](https://develop.sentry.dev/sdk/data-model/event-payloads/contexts/#runtime-context)

Including the runtime context issue stream probably requires the following changes:
- Changing the `issues` endpoint: `OrganizationGroupIndexEndpoint`
- Including `runtime` to the data here (is returned in the `issues` endpoint): https://github.com/getsentry/sentry/blob/af33c2a5cc89a7cb5b5fb9307ee40cbddc5677c2/src/sentry/models/group.py#L598-L600
- Getting the runtime on Relay and adding it to the data dict mentioned above.

related to https://github.com/getsentry/sentry/issues/85732

Start with the OrganizationGroupIndexEndpoint and the runtime data returned from src/sentry/models/group.py around lines 598-600. Trace how Relay supplies runtime data and how the issues endpoint builds its response, using the Runtime Context developer documentation as the data-model reference. Done means issue stream items show the Frontend or Backend runtime label for JS SDK issues.

Written by the indexing model from the issue text.