Support ProxyAuthScheme

[dagnir]

This commit Adds a ProxyAuthScheme configuration option in ProxyConfiguration and adds support for NEGOTIATE auth scheme.

For backwards compatibility, if username and password are set on the config and the proxy auth scheme is not set, the client assumes BASIC auth scheme. If NEGOTIATE is configured, username and password are ignored.

Motivation and Context

Modifications

Testing

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Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

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• I have read the CONTRIBUTING document
• Local run of mvn install succeeds
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• I have updated the Javadoc documentation accordingly
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• My change is to implement 1.11 parity feature and I have updated LaunchChangelog

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