Fix year zero in dates

[dirkkul]

Closes #1093

Weaviate accepts dates based on RFC3339 which allows the year zero ("0000-01-30T00:00:00Z"). However the datetime library is based on the gregorian calendar which does not have a year zero.

To fix parsing problems we will return years with 0 as the minimum date that is possibel in datetime (datetime.datetime(1, 1, 1, 0, 0)) and emit a warning.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.56%. Comparing base (42fb96c) to head (7ee5338).
Report is 88 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1153      +/-   ##
==========================================
- Coverage   94.68%   94.56%   -0.13%     
==========================================
  Files         190      193       +3     
  Lines       18932    19221     +289     
==========================================
+ Hits        17926    18176     +250     
- Misses       1006     1045      +39     

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