Fixes #23235: missing execution of an IOResult in parent ticket

[fanf]

https://issues.rudder.io/issues/23235

the core problème was that :

                path <- sanitizePath(dest.replaceFirst("/", "") + '/' + file.fileName, basePath)
              } yield {
                for {
                  in  <- file.fileStream.autoClosed
                  out <- path.newOutputStream.autoClosed
                } yield {
                  in.pipeTo(out)
               }

is an IOResult and not a value, so the side effect that used to process the uploaded file was not executed anymore.

The PR also:

• simplify the useless effectM (since we don't have to lift code here, we are already in the good world with sanitizePath)
• add some check in the number of uploaded files. Before that, if several were uploaded, then the last (decided by some code in some lib) used to win. Now it's an error.

[Normation-Quality-Assistant]

This PR is not mergeable to upper versions.
Since it is "Ready for merge" you must merge it by yourself using the following command:
rudder-dev merge https://github.com/Normation/rudder/pull/4965
-- Your faithful QA
Kant merge: "To be is to do."
(https://ci.normation.com/jenkins/job/merge-accepted-pr/71999/console)

[amousset]

OK, merging this PR