BF: don't sys.exit if argparse finds unknown args

[peircej]

argparse.parse_args() does a sys_exit if it finds unknown args, even if exit_on_error=False which is too agressive for our needs

Instead, use parse_known_args and then select the known args set

[codecov]

Codecov Report

Merging #6118 (8b9481a) into dev (e4b5242) will increase coverage by 1.58%.
Report is 58 commits behind head on dev.
The diff coverage is 67.38%.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #6118      +/-   ##
==========================================
+ Coverage   50.59%   52.18%   +1.58%     
==========================================
  Files         333      334       +1     
  Lines       61289    61460     +171     
==========================================
+ Hits        31009    32072    +1063     
+ Misses      30280    29388     -892     

Components	Coverage Δ
app	∅ <ø> (∅)
boilerplate	∅ <ø> (∅)
library	∅ <ø> (∅)
vm-safe library	∅ <ø> (∅)