Flatten command field types for the jsonpacker

[JSCU-CNI]

This PR flattens the field type command in the JSON packer and fixes #132.

Currently the dissect.target project is inconsistent in using the same field name command and the new field type command. This patch makes it possible to upload and aggregate on different records in Elasticsearch with the field name command and differing field types.

For example, see RunKeysPlugin.runkeys and PowerShellHistoryPlugin.powershell_history.

You could argue (and we agree) that this should be fixed in dissect.target as all RecordDescriptors currently using ("string", "command") should perhaps use the new command record type. That makes sense to do in the long run. Perhaps a field called full could be added to the standard output of the command fieldtype dict to still be able to index the full, original, command.

Historically the command field type introduced a backwards incompatible change into dissect. This PR fixes that inconsistency.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.71%. Comparing base (1701dcf) to head (d1ba5ce).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #130   +/-   ##
=======================================
  Coverage   83.70%   83.71%           
=======================================
  Files          34       34           
  Lines        3485     3487    +2     
=======================================
+ Hits         2917     2919    +2     
  Misses        568      568           

Flag	Coverage Δ
unittests	83.71% <100.00%> (+<0.01%)	⬆️

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[Miauwkeru]

Thanks for your contribution, we will look at the changes later. But for now, could you maybe create an issue and attach it to this PR? It would make keeping track of issues a lot easier for us.