Define best practices for big complex queries for Apollo client

[Simply007]

There are multiple issues that cause the query to be too complex and hit the 8KB request size limit, but these are the ones connected to Apollo client specifically:

1. Currently it is possible in graphql load linked content items using ˙_Item˙, but the Apollo client that is used here does not map the response data back - see Apollo misses populating properties when fragments are spread apollographql/apollo-client#7648 (comment)
2. Landing page query is was too complex because it is basically a container for multiple types of sections with different properties (Features Section, Content section, ...) and Landing page query is covering all possible types - this leads to a huge query.
   • Current fix is to disable adding __typename to every object type (default Apollo client behavior) and place __typename only to places where it is absolutely necessary - fixed in 5eb2494
   • If the first problem is fixed, there might be another solution - load only section identification properties (codename and language), pas them to section components and the section component itself would be responsible data fetching. - partly fixed in 5eb2494