feat(cli): credentials system uses AWS SDK v3

[otaviomacedo]

Changes (for now)

• New package, cdk-credential-provider (provisional name), that serves as an API contract for plugin writers.
• The public API exposes a new type CdkCredentials, that replaces AWS.Credentials. The new type is backwards compatible.
• Fix for --proxy command line option. It is just ignored right now.
• Removed PatchedSharedIniFileCredentials. AWS SDK v3 now supports both use cases that motivated the creation of this class: credential_source configuration option, and SSO profiles when reading from a shared credentials file.
• Some tests were testing the implementation details of v2. For example, to make sure that we are getting credentials via the EC2 instance metadata service, we were checking whether Ec2InstanceMetadata.refresh()was being called. Since v3 does things differently, I created a fake metadata service, similar to the Fake STS.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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

[aws-cdk-automation]

The pull request linter has failed. See the aws-cdk-automation comment below for failure reasons. If you believe this pull request should receive an exemption, please comment and provide a justification.

A comment requesting an exemption should contain the text Exemption Request. Additionally, if clarification is needed add Clarification Request to a comment.

[aws-cdk-automation]

The pull request linter fails with the following errors:

❌ Features must contain a change to a README file.
❌ Features must contain a change to an integration test file and the resulting snapshot.
❌ CLI code has changed. A maintainer must run the code through the testing pipeline (git fetch origin pull/31572/head && git push -f origin FETCH_HEAD:test-main-pipeline), then add the 'pr-linter/cli-integ-tested' label when the pipeline succeeds.

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[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 7c46bd9
• Result: FAILED
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