Add datetime[ns, UTC] as understood type

[nils-braun]

Fixes #102

Timezone aware types are still a bit "underrepresented" in dask-sql... This PR at least fixes the issue, but there might be more things to check for in the future

[codecov-io]

Codecov Report

Merging #103 (b5af1b6) into main (40ba2d1) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #103   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           35        35           
  Lines         1460      1464    +4     
  Branches       201       203    +2     
=========================================
+ Hits          1460      1464    +4     

Impacted Files	Coverage Δ
dask_sql/mappings.py	100.00% <100.00%> (ø)

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