Problem: processing directory is not configurable

[jraddaoui]

Is your feature request related to a problem? Please describe.

The download activity places the package in the default temporary directory, as returned by os.TempDir, which reads:

TempDir returns the default directory to use for temporary files.

On Unix systems, it returns $TMPDIR if non-empty, else /tmp. On Windows, it uses GetTempPath, returning the first non-empty value from %TMP%, %TEMP%, %USERPROFILE%, or the Windows directory. On Plan 9, it returns /tmp.

The directory is neither guaranteed to exist nor have accessible permissions.

Additionally, we may want to set it to a different directory for performance reasons, like having a faster filesystem in another path or trying to avoid move operation between shared directories (a3m, preprocessing).

Describe the solution you'd like

I'd like a configuration option to set a processing directory, to be used by the download and other activities that may need it.

Describe alternatives you've considered

None.

Additional context

The initial preprocessing child workflow implementation uses the preprocessing shared path as destination for the downloaded package when preprocessing is enabled (#861).

[jraddaoui]

Kind of related: #864