Add merge strategy fields to Repository model

[dziemba]

Adds:

• allowMergeCommit
• allowRebaseMerge
• allowSquashMerge

[codecov]

Codecov Report

Merging #92 (e33974d) into master (94db54c) will decrease coverage by 0.41%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master      #92      +/-   ##
============================================
- Coverage     70.20%   69.78%   -0.42%     
  Complexity      222      222              
============================================
  Files            36       36              
  Lines           866      854      -12     
  Branches         36       35       -1     
============================================
- Hits            608      596      -12     
  Misses          233      233              
  Partials         25       25              

Impacted Files	Coverage Δ
...thub/v3/repos/BranchProtectionUrlDeserializer.java	100.00% <100.00%> (ø)

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[lufsariskogen]

Looks good