Added configuration for new cugraph-doc-codeowners review group

[rlratzel]

Added configuration for new cugraph-doc-codeowners review group.

This seems to agree with the syntax used elsewhere and described here, but will need to be tested after this is merged (I'm assuming?) by checking PRs that changed specific files to see if the cugraph-doc-codeowners group is added as expected.

[codecov-io]

Codecov Report

Merging #1344 (8cfe7b8) into branch-0.18 (2fb0725) will increase coverage by 0.01%.
The diff coverage is 38.70%.

@@               Coverage Diff               @@
##           branch-0.18    #1344      +/-   ##
===============================================
+ Coverage        60.38%   60.39%   +0.01%     
===============================================
  Files               67       67              
  Lines             3029     3058      +29     
===============================================
+ Hits              1829     1847      +18     
- Misses            1200     1211      +11     

Impacted Files	Coverage Δ
python/cugraph/centrality/__init__.py	100.00% <ø> (ø)
python/cugraph/structure/graph.py	67.18% <0.00%> (+0.38%)	⬆️
python/cugraph/utilities/utils.py	66.92% <18.18%> (-4.63%)	⬇️
python/cugraph/dask/common/input_utils.py	23.07% <28.57%> (+1.14%)	⬆️
python/cugraph/dask/common/mg_utils.py	37.50% <38.09%> (-2.50%)	⬇️
python/cugraph/community/spectral_clustering.py	72.54% <38.46%> (-11.67%)	⬇️
python/cugraph/structure/number_map.py	58.12% <50.00%> (+2.16%)	⬆️
python/cugraph/__init__.py	100.00% <100.00%> (ø)
...ython/cugraph/centrality/betweenness_centrality.py	100.00% <100.00%> (ø)
python/cugraph/linear_assignment/__init__.py	100.00% <100.00%> (ø)
... and 2 more

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