Cache queries of gateway to course service when fetching information about courses the user is a member of

[Nimeggis]

From graphql_gateway created by myluki2000: IT-REX-Platform/graphql_gateway#57

Description

For every query of the frontend to the gateway authenticates the user and fetches the course memberships of the user and also data (pubished?, startdate, enddate) about the courses the user is a member of (by querying the course service).

These data usually do not change from one query to the next, so they could be cached in the gateway so it doesn't have to call the course service on each request.