BUG: Add band_as_variable to xarray plugin

[snowman2]

Continuation of #600

[codecov]

Codecov Report

Base: 96.33% // Head: 96.33% // No change to project coverage 👍

Coverage data is based on head (0934fa3) compared to base (9643b46).
Patch has no changes to coverable lines.

❗ Current head 0934fa3 differs from pull request most recent head 75626a9. Consider uploading reports for the commit 75626a9 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #603   +/-   ##
=======================================
  Coverage   96.33%   96.33%           
=======================================
  Files          11       11           
  Lines        1691     1691           
=======================================
  Hits         1629     1629           
  Misses         62       62           

Impacted Files	Coverage Δ
rioxarray/xarray_plugin.py	91.30% <ø> (ø)

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[snowman2]

Thanks @justingruca 👍