This commit updates `TaskExecutionAutoConfiguration` to permit the
auto-configuration of a `TaskExecutor` even if a user-defined `Executor`
bean is present.
Such `Executor` may have been created for totally unrelated reason, and
it may or may not be an `AsyncTaskExecutor`. The default behavior has
not changed, but this commit provides a new property,
`spring.task.execution.mode` that can be set to `force` to
auto-configure the `TaskExecutor` anyway.
Because this mode made it so that two `Executor` will be present in the
context, this commit also automatically configures an `AsyncConfigurer`
if none is present already to make sure task processing uses the
auto-configured TaskExecutor.
Closes gh-44659
13bd61445b