Add Repo feature

[punit-kulal]

PUT /repositories/{repository_name} route implements an idempotent route to add or update(using force_update flag) a repository for albatross.
Have added corresponding tests.
yaml and flock dependencies have been added to support read, edit of underlying config files

[codecov-commenter]

Codecov Report

Merging #11 (2613b4d) into master (60b7ecc) will decrease coverage by 0.32%.
The diff coverage is 72.25%.

@@            Coverage Diff             @@
##           master      #11      +/-   ##
==========================================
- Coverage   73.60%   73.27%   -0.33%     
==========================================
  Files          17       21       +4     
  Lines         538      711     +173     
==========================================
+ Hits          396      521     +125     
- Misses        111      145      +34     
- Partials       31       45      +14     

Impacted Files	Coverage Δ
pkg/helmcli/repository/adder.go	64.89% <64.89%> (ø)
api/repository/add.go	66.66% <66.66%> (ø)
api/repository/service.go	96.55% <96.55%> (ø)
pkg/helmcli/repository/client.go	100.00% <100.00%> (ø)

[kaustubhkurve]

Also, in the PR description, the route is mentioned as /repository/{repository-name}. However, it's /repositories/{repository-name}. You can update the description as well.

[kaustubhkurve]

A