Add enode link URL endpoint

[AndrewLester]

Pull Request

Description

Adds an endpoint for getting a valid Enode link URL for a user.

Fixes #72

Need to use env vars for Enode URLs, but coming in another PR

How Has This Been Tested?

Adds a test for both fake and mock Enode requests.

• [x] Yes

Checklist:

• [x] My code follows OCF's coding style guidelines
• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have checked my code and corrected any misspellings

[codecov[bot]]

Codecov Report

Merging #86 (d26af24) into h4i/enode (1a23431) will increase coverage by 5.04%. The diff coverage is 100.00%.

:exclamation: Current head d26af24 differs from pull request most recent head baa189b. Consider uploading reports for the commit baa189b to get more accurate results

@@              Coverage Diff              @@
##           h4i/enode      #86      +/-   ##
=============================================
+ Coverage      86.93%   91.97%   +5.04%     
=============================================
  Files              9        8       -1     
  Lines            398      324      -74     
=============================================
- Hits             346      298      -48     
+ Misses            52       26      -26     

Impacted Files	Coverage Δ
pv_site_api/fake.py	100.00% <100.00%> (ø)
pv_site_api/main.py	90.18% <100.00%> (+0.18%)	:arrow_up:

... and 4 files with indirect coverage changes

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