Support building without cugraph-ops

[ChuckHastings]

Add -DUSE_CUGRAPH_OPS=OFF option for building where you can't access cugraph-ops. By default USE_CUGRAPH_OPS is set to ON.

If USE_CUGRAPH_OPS is set to OFF then the software will build without those features. At runtime functions that rely on cugraph-ops (currently this is only uniform neighborhood sampling) will fail with an exception.

[codecov-commenter]

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@@               Coverage Diff               @@
##             branch-22.08    #2405   +/-   ##
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  Hits                    ?     3099           
  Misses                  ?     2056           
  Partials                ?        0           

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[ChuckHastings]

@gpucibot merge