Add Azure Key Vault provider

[s12v]

No description provided.

[codecov]

Codecov Report

Merging #6 into master will decrease coverage by 2.36%.
The diff coverage is 61.11%.

@@            Coverage Diff             @@
##           master       #6      +/-   ##
==========================================
- Coverage   70.64%   68.27%   -2.37%     
==========================================
  Files           4        5       +1     
  Lines         109      145      +36     
==========================================
+ Hits           77       99      +22     
- Misses         24       33       +9     
- Partials        8       13       +5

Impacted Files	Coverage Δ
provider/azurekeyvault/azurekeyvault.go	61.11% <61.11%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2527a48...34da2da. Read the comment docs.