fix: typos in JSON annotations caught by staticcheck

[mboersma]

Reason for Change:
Trying to fix #2839, I ran golangci-lint with the default linters enabled and couldn't ignore these typos. But I wonder if this could create actual backward-compatibility issues if the previous annotations weren't being honored as expected.

Issue Fixed:

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[codecov]

Codecov Report

Merging #3104 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3104   +/-   ##
=======================================
  Coverage   70.87%   70.87%           
=======================================
  Files         147      147           
  Lines       25472    25472           
=======================================
  Hits        18053    18053           
  Misses       6290     6290           
  Partials     1129     1129           

Impacted Files	Coverage Δ
pkg/api/vlabs/types.go	73.30% <ø> (ø)

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[jackfrancis]

@mboersma I think this should be safe because the back-compat input scenario would include the JSON-rendered zero values already present. And those zero values should still be acceptable as aks-engine input.

@devigned @CecileRobertMichon for sanity check