Fileset format for parquet inputs

[alexander-held]

Describe the bug
The expected fileset format for parquet inputs differs from the usual format used with ROOT files. For a processor.Runner with format="parquet", the expected format is

{"name": [list_of_files]}

while for other cases

{"name": {"files": [list_of_files], "metadata": {"some_metadata": 123}}

is supported (which is the more powerful format, as it allows to conveniently feed metadata to processors).

To Reproduce
Run run_parquet_job or a runner with format="parquet" using a fileset containing metadata.

Expected behavior
Same fileset format including metadata is supported.

Output

ValueError: For in-memory datasets, you cannot pass any additional arguments

Desktop (please complete the following information):
n/a

Additional context
n/a