chore: add unit test coverage thresholds

[alharris-at]

Description of changes

Add unit test coverage thresholds (currently set to min(curr_val, 80)) to prevent reduction in unit test coverage.

Info on the coverage configuration can be found here https://jestjs.io/docs/27.x/configuration#coveragethreshold-object

Line coverage refers to what % of lines are covered in the given package (in average across all files, since we're using global)
Branch coverage refers to what % of code paths are covered in the given package (in average across all files, since we're using global)
Function coverage refers to what % of functions are covered in the given package (in average across all files, since we're using global)

Issue #, if available

N/A

Description of how you validated changes

Ran unit tests.

Checklist

• PR description included
• yarn test passes

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 #609 (6066698) into main (21bbff8) will increase coverage by 0.02%.
The diff coverage is 100.00%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

@@            Coverage Diff             @@
##             main     #609      +/-   ##
==========================================
+ Coverage   85.92%   85.94%   +0.02%     
==========================================
  Files         152      152              
  Lines        7493     7490       -3     
  Branches     1959     1957       -2     
==========================================
- Hits         6438     6437       -1     
+ Misses        962      960       -2     
  Partials       93       93              

Impacted Files	Coverage Δ
...codegen/src/codegen-config/AmplifyCodeGenConfig.js	47.50% <100.00%> (+0.51%)	⬆️
...ckages/amplify-codegen/src/codegen-config/index.js	95.23% <100.00%> (ø)

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more