New boefje containerized setup ignores stderr

[zcrt]

Describe the bug
There are some boefjes using a subprocess call that captures both stderr and stdout. However, often stderr is ignored and only stdout is returned. This makes debugging a badly functioning boefje hard.

Expected behavior
Storing both stderr and stdout (and possibly even stdin) securely.

Examples

nl-kat-coordination/boefjes/boefjes/plugins/kat_dnssec/main.py

Line 20 in 2583519

return [(set(), output.stdout)]

nl-kat-coordination/boefjes/boefjes/plugins/kat_nmap_tcp/main.py

Line 21 in 2583519

return [(set(), subprocess.run(cmd, capture_output=True).stdout.decode())]

[underdarknl]

Adding stderror to the output stream seems logical. however, that needs to be done on a 'per boefje' basis.
Returning stdout also makes better sense than parsing the output in the boefje itself, and then presenting a reworked version to the normalizer, as I'd rather keep the original output on file and work with that.
We do need to make sure that we can differentiate between the wanted (stdout) output, and the unwanted (stderror) output, as both these raw files will receive the boefje/$boefjename mimetype.

[underdarknl]

related #1373