refactor graphql.NoCache. use string type keys

[adomaskizogian]

Fixes: #3331

All internal uses of cache use string type keys and leaves out the value type as generic parameter. The new generic NoCache implementation only allows specifying the key type and the value type is a pointer of the key type. Meaning if I specify the key type string the value type is *string. This implementation cannot be assigned in place of graphql.Cache[any]

I propose to fix this by updating the NoCache definition by dropping the key type and allowing to use only string as key, any as value

See #3179

[coveralls]

coverage: 58.869% (-0.05%) from 58.915%
when pulling 4a7efdd on adomaskizogian:master
into 96429c1 on 99designs:master.

[StevenACoffman]

Thanks!