Fix .command.stage file write when using Google Cloud

[jorgee]

close #5888

.command.stage file is created when stage script is larger than 1MB and stage file is in the default filesystem. In the case of Google Batch executor, the stage file is /mnt/xxx/ because of the gcsfuse. Later, it tries to write the file that doesn't exist in the head node, so it fails. It is mainly due to the targetStage file returns the mount path instead of the remote path as for .command.run, etc.

In this PR, I have fixed the error by returning he remote version of the stage file instead of the localone when requesting the targetStageFile.

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[bentsherman]

Ideally it should not write the stage script at all for google batch. That was the intention of this check:

nextflow/modules/nextflow/src/main/groovy/nextflow/executor/BashWrapperBuilder.groovy

Lines 275 to 282 in 53c28b8

	// enable only when the stage uses the default file system, i.e. it's not a remote object storage file
	// see https://github.com/nextflow-io/nextflow/issues/4279
	if( stageFile.fileSystem == FileSystems.default && stagingScript.size() >= stageFileThreshold.bytes ) {
	stageScript = stagingScript
	return header + "bash ${stageFile}"
	}
	else
	return header + stagingScript

But I didn't consider that the google batch script launcher overwrites the task workDir to be the local container-mounted path. So I'm not sure if there is a clean way to fix this check