Migrate configuration command from mihextras extention

[mih]

Fixes #5489

The individual commits following the first one are improvements over the extension version.

Changelog

💫 Enhancements and new features

• A new configurationcommand provides an interface to manipulate and query the DataLad configuration.
  • Unlike the global Python-only datalad.cfg or dataset-specific Dataset.config configuration managers, this command offers a uniform API across the Python and the command line interfaces.
  • This command was previously available in the mihextras extension as x-configuration, and has been merged into the core package in an improved version. #5489 (by @mih)
  • In its default dump mode, the command provides an annotated list of the effective configuration after considering all configuration sources, including hints on additional configuration settings and their supported values.

📝 Documentation

• The documentation of the configuration command now details all locations DataLad is reading configuration items from, and their respective rules of precedence (by @mih)

[codecov]

Codecov Report

Merging #6306 (27e4119) into master (9aa3a8c) will increase coverage by 0.05%.
The diff coverage is 98.36%.

@@            Coverage Diff             @@
##           master    #6306      +/-   ##
==========================================
+ Coverage   89.84%   89.89%   +0.05%     
==========================================
  Files         331      333       +2     
  Lines       43155    43339     +184     
==========================================
+ Hits        38773    38961     +188     
+ Misses       4382     4378       -4     

Impacted Files	Coverage Δ
datalad/interface/__init__.py	100.00% <ø> (ø)
datalad/interface/common_cfg.py	100.00% <ø> (ø)
datalad/local/configuration.py	97.90% <97.90%> (ø)
datalad/local/tests/test_configuration.py	100.00% <100.00%> (ø)
datalad/ui/dialog.py	89.83% <0.00%> (+2.13%)	⬆️
datalad/local/subdatasets.py	96.09% <0.00%> (+2.34%)	⬆️

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[adswa]

I think with #6349 merged, this PR can be rebased. #6312 makes it sound like this would resolve the current error on CrippledFS.

[mih]

I think with #6349 merged, this PR can be rebased. #6312 makes it sound like this would resolve the current error on CrippledFS.

Oh, these are unexpectedly good news. I was about to close this PR and to continue working on this command in the extension

[mih]

Pushed a rebase.

[codeclimate]

Code Climate has analyzed commit 27e4119 and detected 25 issues on this pull request.

Here's the issue category breakdown:

Category	Count
Complexity	7
Bug Risk	5
Style	13

View more on Code Climate.