Issue #, if available:

Description of changes:

This PR enhances STSProfileCredentialsProvider to support reading web_identity_token_file values from config files and if provided, perform an AssumeRoleWithWebIdentity operation to acquire credentials.

Let me know what kind of testing I should add for this.

Check all that applies:

• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
• Checked if this PR will not introduce cross-platform inconsistent behavior.
• Checked if this PR would require a ReadMe/Wiki update.

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