feat(aws_auth): Add support of awsSecurityCredentialsSupplierClass in ExternalAccountCredentials when create from GcpCredentials from file.

[GrigorievNick]

Add support of awsSecurityCredentialsSupplierClass in ExternalAccountCredentials when creating GcpCredentials from the file.

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Fixes #1408

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[conventional-commit-lint-gcf]

🤖 I detect that the PR title and the commit message differ and there's only one commit. To use the PR title for the commit history, you can use Github's automerge feature with squashing, or use automerge label. Good luck human!

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[GrigorievNick]

@googleapis-stewards, how can I get any feedback?

[lqiu96]

@lsirac @googleapis/aion-sdk I think this change would be better to be reviewed by you all. If you feel otherwise, I can take a look.