feat: add API extension headless config

[marcvberg]

Description of changes

Add config option to API headless for extending API keys

Issue #, if available

https://github.com/aws-amplify/amplify-category-api/issues/598

Description of how you validated changes

No functional changes yet, this is an optional addition to headless input

Checklist

• [ ] PR description included
• [ ] yarn test passes
• [ ] Tests are changed or added
• [ ] Relevant documentation is changed or added (and PR referenced)
• [ ] New AWS SDK calls or CloudFormation actions have been added to relevant test and service IAM policies

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

[codecov-commenter]

Codecov Report

Merging #11037 (9ef6f48) into dev (a8fad87) will increase coverage by 0.00%. The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev   #11037   +/-   ##
=======================================
  Coverage   49.43%   49.43%           
=======================================
  Files         688      688           
  Lines       33360    33360           
  Branches     6830     6830           
=======================================
+ Hits        16491    16492    +1     
+ Misses      15347    15346    -1     
  Partials     1522     1522           

Impacted Files	Coverage Δ
...li/src/domain/amplify-usageData/getUsageDataUrl.ts	100.00% <0.00%> (+12.50%)	:arrow_up:

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[marcvberg]

Good catch, needed to update the pick for update api

[danielleadams]

Running integration tests, and then this will be ready to merge.

[danielleadams]

I've restarted the integration tests. Once they pass, I will approve.