feat(experimentalIdentityAndAuth): add @aws.auth#sigv4 integration tests

[syall]

Issue #, if available:

N/A.

Description of changes:

Dependent on: #1018, #1021

Add @aws.auth#sigv4 integration tests.

• Thread sigv4 cases

Testing:

In staging, not all NPM packages are officially published, so the following replacement is necessary in the smithy-typescript-codegen-test projections:

# Replace
"@smithy/experimental-identity-and-auth"
# with the local `node_modules/` path, e.g.
"/Users/yuasteve/development/ts-ia/smithy-typescript/node_modules/@smithy/experimental-identity-and-auth"

1. Run ./gradlew :smithy-typescript-codegen-test:clean :smithy-typescript-codegen-test:build
2. Do the replacement mentioned above
3. Run node scripts/build-generated-test-packages.js (may need to do more than once...)
4. Ran yarn test:integration in @smithy/experimental-identity-and-auth

If one or more of the packages in the /packages directory has been modified, be sure yarn changeset add has been run and its output has
been committed and included in this pull request. See CONTRIBUTING.md.

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