Merge branch 'ld-docs-link-graphql-performance' into 'master'

Add GraphQL performance optimization link

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/170373



Merged-by: Luke Duncalfe <lduncalfe@gitlab.com>

doc/development/feature_development.md

@@ -122,6 +122,7 @@ Consult these topics for information on contributing to specific GitLab features
   masked by query caching, memory profiling and why should we avoid cached
   queries.
 - [JSON guidelines](json.md) for how to handle JSON in a performant manner.
+- [GraphQL API optimizations](api_graphql_styleguide.md#optimizations) for how to optimize GraphQL code.
 
 ## Database guides