Add create achievement GraphQL mutation

app/controllers/uploads_controller.rb

app/graphql/mutations/achievements/create.rb

app/graphql/types/achievements/achievement_type.rb

app/graphql/types/mutation_type.rb

app/graphql/types/namespace_type.rb

app/policies/achievements/achievement_policy.rb

app/policies/group_policy.rb

app/services/achievements/base_service.rb

app/services/achievements/create_service.rb

config/feature_flags/development/achievements.yml

config/routes/uploads.rb

doc/api/graphql/reference/index.md

spec/controllers/uploads_controller_spec.rb

spec/graphql/mutations/achievements/create_spec.rb

spec/graphql/types/achievements/achievement_type_spec.rb

spec/graphql/types/namespace_type_spec.rb

...equests/api/graphql/mutations/achievements/create_spec.rb

spec/services/achievements/create_service_spec.rb

...t/shared_contexts/policies/group_policy_shared_context.rb