[REVIEW] Katz Centrality : Auto calculation of alpha parameter if set to none

[kaatish]

Fixes #730

• Katz will automatically calculate alpha parameter if it is not provided by the user
• The code will no longer inform the user if the value of alpha is greater than the minimum alpha for convergence
• The code will no longer inform the user if the centrality calculation does not converge

[GPUtester]

Please update the changelog in order to start CI tests.

View the gpuCI docs here.

[codecov-io]

Codecov Report

Merging #862 into branch-0.14 will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           branch-0.14     #862   +/-   ##
============================================
  Coverage        47.66%   47.66%           
============================================
  Files               44       44           
  Lines             1328     1328           
============================================
  Hits               633      633           
  Misses             695      695           

Impacted Files	Coverage Δ
python/cugraph/centrality/katz_centrality.py	100.00% <ø> (ø)

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