Add Louvain to the C API

[ChuckHastings]

This PR adds Louvain to the C API. This PR is a full implementation including:

• C API definition
• C API implementation calling the C++ version of Louvain
• SG and MG unit tests exercising the Louvain implementation
• A small documentation update to triangle counting that was discovered in the final review of the triangle counting C API PR

[codecov-commenter]

Codecov Report

Merging #2292 (f7b3e67) into branch-22.06 (046cbd2) will decrease coverage by 0.17%.
The diff coverage is 44.66%.

❗ Current head f7b3e67 differs from pull request most recent head 5cd323d. Consider uploading reports for the commit 5cd323d to get more accurate results

@@               Coverage Diff                @@
##           branch-22.06    #2292      +/-   ##
================================================
- Coverage         63.97%   63.80%   -0.18%     
================================================
  Files               100      100              
  Lines              4436     4481      +45     
================================================
+ Hits               2838     2859      +21     
- Misses             1598     1622      +24     

Impacted Files	Coverage Δ
python/cugraph/cugraph/dask/community/louvain.py	24.24% <0.00%> (-1.57%)	⬇️
python/cugraph/cugraph/dask/link_analysis/hits.py	18.75% <0.00%> (ø)
...aph/cugraph/dask/sampling/neighborhood_sampling.py	0.00% <0.00%> (ø)
python/cugraph/cugraph/dask/traversal/bfs.py	14.75% <0.00%> (-1.92%)	⬇️
python/cugraph/cugraph/dask/traversal/sssp.py	21.42% <0.00%> (-1.08%)	⬇️
python/cugraph/cugraph/structure/number_map.py	65.83% <6.66%> (-0.96%)	⬇️
...ure/graph_implementation/simpleDistributedGraph.py	23.02% <42.85%> (+0.42%)	⬆️
python/cugraph/cugraph/traversal/bfs.py	78.87% <58.33%> (-7.13%)	⬇️
...ython/cugraph/cugraph/community/ktruss_subgraph.py	88.23% <100.00%> (+2.94%)	⬆️
python/cugraph/cugraph/community/leiden.py	100.00% <100.00%> (+7.69%)	⬆️
... and 7 more

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[seunghwak]

So, when can we delete the legacy Louvain? After python updates?

[ChuckHastings]

@gpucibot merge