Breaking: include DataType in CategoricalEltypes

[tiemvanderdeure]

Does what it says on the tin :)

Specifically designed to make using RasterDataSources climate types as lookups (as in rafaqz/Rasters.jl#826) even more slick.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.64%. Comparing base (a5585f5) to head (8636f9c).
Report is 40 commits behind head on breaking.

Additional details and impacted files

@@             Coverage Diff              @@
##           breaking     #876      +/-   ##
============================================
+ Coverage     83.66%   84.64%   +0.98%     
============================================
  Files            47       50       +3     
  Lines          4653     4683      +30     
============================================
+ Hits           3893     3964      +71     
+ Misses          760      719      -41     

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[rafaqz]

Does what it says on the tin :)

Oh no it's spreading 😂

But yes, great idea. Technically breaking I guess as it's changing the returned type, so let's lump this with another break