Update call sites of ExternalServicesStore.List to avoid application-level aggregation

Created by: unknwon

... over all external services, instead accomplish via SQL query.

TODOs (selective list of this query):

• externalServiceKinds #12779
• handleConfigOverrides #12781

Refs:

• https://sourcegraph.com/github.com/sourcegraph/sourcegraph@5d73f94a7ad9c8c5a5d30954f737e9dde5c2a8b5/-/blob/internal/db/external_services.go#L405

Part of #12699 (closed).