Revisit how applicationTaskExecutor is utilized across various Spring integrations

The current setup seems complex and might need reconsideration.

Spring MVC, Spring WebFlux, and Spring GraphQL all rely on a bean named
applicationTaskExecutor. For Spring MVC and Spring WebFlux (spring.threads.virtual.enabled=true), this bean must be of type AsyncTaskExecutor, whereas Spring GraphQL requires a bean of type Executor.

Spring WebSocket and JPA will use an AsyncTaskExecutor if either a single bean of this
type is available or if a bean named applicationTaskExecutor is defined.

I suggest revisiting the WebSocketMessageConverterConfiguration and
JpaRepositoriesAutoConfiguration configurations to align them with Spring MVC,
Spring WebFlux, and Spring GraphQL.

I am uncertain about GraphQL as it uses applicationTaskExecutor but with a different
type.

Start by reading WebSocketMessageConverterConfiguration and JpaRepositoriesAutoConfiguration, then trace how applicationTaskExecutor is selected by the Spring MVC, WebFlux, and GraphQL integrations described in the issue. Resolve the Executor versus AsyncTaskExecutor expectations before changing either configuration. Done means the WebSocket and JPA configurations have an agreed, consistent executor-selection behavior with the other integrations.