feat: Add EC per request functionality

[rishav-karanjit]

Description

add per request EC functionality

Motivation and Context

This is because it makes sense for use of encryption context to be send per request.

Testing

Tested with the CI I had in private https://github.com/aws/private-amazon-s3-encryption-client-dotnet-staging/pull/9

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

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

License

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