add scaling policy endpoint

[nikita-b]

I added scaling-policies endpoints:
https://developer.hashicorp.com/nomad/api-docs/scaling-policies#read-scaling-policy

I can add more tests, but we need merge PR with scaling related operations: #131

[codecov-commenter]

Codecov Report

Merging #136 (dce5157) into master (690add1) will decrease coverage by 0.14%.
The diff coverage is 84.00%.

@@            Coverage Diff             @@
##           master     #136      +/-   ##
==========================================
- Coverage   90.61%   90.47%   -0.15%     
==========================================
  Files          27       28       +1     
  Lines        1130     1155      +25     
==========================================
+ Hits         1024     1045      +21     
- Misses        106      110       +4     

Impacted Files	Coverage Δ
nomad/api/scaling.py	80.00% <80.00%> (ø)
nomad/__init__.py	98.36% <100.00%> (+0.05%)	⬆️
nomad/api/__init__.py	100.00% <100.00%> (ø)

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[nikita-b]

@jonathanrcross @jrxFive Could we fix or disable Publish Test PyPi step? CI is broken because of it :(

[jonathanrcross]

It took me awhile to realize that the "failure" is due to pypa/gh-action-pypi-publish#49. I'll add the push event that should fix this from failing.

[nikita-b]

@jonathanrcross Thanks!