Update cors doco

[adanilev]

Issue #, if available:
The documentation does not mention the AddDefaultAuthorizerToCorsPreflight property that was added in #828.

Description of changes:

• Added the AddDefaultAuthorizerToCorsPreflight parameter to the Template Specification doc
• Added an example app that uses the DefaultAuthorizer + CORS.

Description of how you validated changes:
Deployed the resources and called the API.

Checklist:

• Write/update tests
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected
• Add/update example to examples/2016-10-31

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #1079 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #1079   +/-   ##
========================================
  Coverage    94.81%   94.81%           
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  Files           69       69           
  Lines         3276     3276           
  Branches       639      639           
========================================
  Hits          3106     3106           
  Misses          89       89           
  Partials        81       81

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[praneetap]

Thanks for adding the example and fixing the docs! Really appreciate the contribution 👍

[danludwig]

When will this go to master? I searched the docs @ https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md trying to find this and didn't realize I had to switch to the develop branch.

[keetonian]

@danludwig Yes, this will be merged into master soon with our v1.15.0 release.