Add GraphQL operation name to caller_id for endpoint targeting

What does this MR do and why?

Add GraphQL operation name to caller_id for endpoint targeting. Currently GraphQL caller_id is always GraphqlController#execute which is not very useful. This MR will add the operation name as a suffix such as GraphqlController#execute:getProjects. This brings GraphQL in line with REST endpoints.

Benefits:

• Enable feature flags for specific GraphQL operations
• Opt-out problematic queries during incidents
• Gradual rollout of GraphQL performance improvements
• Better observability in Kibana by operation name

Example usage with endpoint actors:

  # Target specific GraphQL operation
  Feature.enable(:cache_projects, Feature.endpoint('GraphqlController#execute:getProjects'))

  # Opt-out slow query during incident
  Feature.opt_out(:expensive_feature, Feature.endpoint('GraphqlController#execute:getAllIssues'))

The operation name is extracted from the operationName parameter sent by GraphQL clients and appended to the base caller_id in a before_action.

Feature flag: This change is behind the graphql_caller_id_with_operation_name feature flag to allow safe rollout and ensure existing systems that depend on the exact caller_id format are not disrupted.

Related to !216754 (merged)

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