Currently, TaskExecutor only has a scheduleRemoteCommand interface that takes a callback and returns a callback handle.

As we are structuring more code as a future chain that runs on an executor with a limited number of threads (particularly Primary-Only Service instances), it will be very helpful to have a version of scheduleRemoteCommand that returns a Future.

This, combined with the generic whenAll/whenAny/collect utilities described in SERVER-50341, would be very useful in writing a Primary-Only Service which has steps that send a command to many remote nodes and wait for all of their responses.

Note that SERVER-50342, which is to add a version of Shard::runCommand that returns a Future, would help in sharding code, but would not help for code that runs in standalone replica sets, such as the Primary-Only Services being built for Multitenant Migrations for Serverless (PM-1791).

While this is not an immediately blocking work on PM-1791, since we can work around it by blocking the thread on the executor while waiting for a network response, it does block releasing PM-1791.