Backend: GraphQL type and resolver for agent config

MR: Add agent config type, resolve, finder with per... (!158587 - merged)

Description

This issue is created as the follow up on the thread here, #427519 (comment 1985555517)

we are going to have a new type for the remote_development_agent_configs under ee/app/graphql/types/remote_development (like ee/app/graphql/types/remote_development/workspace_type.rb), and then set up the correct connections/resolvers to make it work and have its fields be retrievable in a single query like you have above.

And we would like to do the similar thing for remote_development_namespace_cluster_agent_mappings as well

Acceptance Criteria

• all the types/resolvers/connections/policy files available for remote_development_agent_configs as planned
• also tested everything works fine locally
• Update ee/spec/requests/remote_development/integration_spec.rb to exercise and assert on the newly-added fields.

Technical Requirements

Pls see this MR for more implementation details. It initially used as a spike for understanding technical details.

Add agent config type, resolve, finder with per... (!158587 - merged)