Add ServiceURL option for KMS client

[bdurrani]

AmazonKeyManagementServiceConfig doesn't use the service url when it's setting on AmazonS3CryptoConfigurationV2

Description

Motivation and Context

I'm using LocalStack when I set ServiceURL on AmazonS3CryptoConfigurationV2 I'm seeing the Kms calling aws endpoint

See #29 for reference

Testing

Screenshots (if appropriate)

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [x] My code follows the code style of this project
• [ ] My change requires a change to the documentation
• [ ] I have updated the documentation accordingly
• [x] I have read the README document
• [ ] I have added tests to cover my changes
• [ ] All new and existing tests passed

License

• [x] I confirm that this pull request can be released under the Apache 2 license

[bdurrani]

@normj Hi there Is this change ok for the KMS client ServiceURL option? As discussed here: https://github.com/aws/amazon-s3-encryption-client-dotnet/pull/29

Thanks

[ashovlin]

I've merged this to dev, which is our staging branch for the next release. We'll reply again once the new release is out.

[ashovlin]

This PR was released yesterday in 2.1.0, thanks again for your contribution!