create: backport implementation --stdin-mode, --stdin-user and --stdin-group, #5462

[schors]

--stdin-mode, --stdin-user and --stdin-group options added
File mode forces to regular file with other values from the option --stdin-mode. Default mode is 0o100660.
Error occurs if given user or group do not exists. Default user and group values are taken from system uid/gid 0

[codecov-io]

Codecov Report

Merging #5466 into 1.1-maint will increase coverage by 0.02%.
The diff coverage is 68.75%.

@@              Coverage Diff              @@
##           1.1-maint    #5466      +/-   ##
=============================================
+ Coverage      80.26%   80.29%   +0.02%     
=============================================
  Files             27       27              
  Lines          10358    10371      +13     
  Branches        1827     1830       +3     
=============================================
+ Hits            8314     8327      +13     
+ Misses          1531     1528       -3     
- Partials         513      516       +3     

Impacted Files	Coverage Δ
src/borg/archive.py	82.75% <42.85%> (+0.21%)	⬆️
src/borg/archiver.py	82.05% <87.50%> (+0.01%)	⬆️
src/borg/constants.py	100.00% <100.00%> (ø)
src/borg/cache.py	85.90% <0.00%> (-0.14%)	⬇️

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[ThomasWaldmann]

Thanks!