Fix datalad special remote error reporting

[bpoldrack]

Utilize CapturedException.format_with_cause instead of a custom solution, potentially leading to an error message containing an uninformative [None].
This would also include more than just the first-level __cause__ (all the way down and include potential __context__ as well)

Closes #7332

With this change the output reported in #7332 (Failed to download from any of 2 locations [None]) changes to:

[{'action': 'get',
  'annexkey': 'MD5E-s994556226--ffc1353e08d640c7ba3154d963573732.nii.gz',
  'error_message': 'Failed to download from any of 2 locations ["Failed to '
                   'acquire lock to establish download session at '
                   '/home/<REDACTED>.cache/datalad/locks/downloader-auth.lck '
                   'in 3 attempts.Check following process: PID=2946262 '
                   'CWD=/var/lib/condor/execute/dir_2944629/tmpwoojnx0_/datadir/HCP1200/567052/MNINonLinear '
... <REDACTED>

So, much more telling.

[yarikoptic]

I don't see complaints from codecov which means that this code block is probably tests covered -- could you add checking for expected cause to appear somewhere where expected in the test?

[bpoldrack]

I don't see where this is covered. test_datalad.py doesn't appear to test retrieval at all.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +1.98 🎉

Comparison is base (c6004a6) 88.71% compared to head (8c7bc10) 90.70%.

Additional details and impacted files

@@            Coverage Diff             @@
##            maint    #7333      +/-   ##
==========================================
+ Coverage   88.71%   90.70%   +1.98%     
==========================================
  Files         327      327              
  Lines       44518    44530      +12     
  Branches     5908     5909       +1     
==========================================
+ Hits        39494    40390     +896     
+ Misses       5009     4125     -884     
  Partials       15       15              

Impacted Files	Coverage Δ
datalad/customremotes/datalad.py	64.28% <0.00%> (+2.64%)	⬆️

... and 14 files with indirect coverage changes

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[yarikoptic-gitmate]

PR released in 0.18.3