Add copyright header to all source files

[brooke-hamilton]

Description
All source files created by Microsoft employees are required to have a copyright header as a comment with the two lines shown below.

# Copyright (c) Microsoft Corporation.
# Licensed under the MIT License.

Note: third party contributors can add their own copyright header so long as they keep all pre-existing copyright notices intact in the files they are contributing. So contributors can add their own copyright header to their original contributions, as well as to files they modify and contribute back to the Microsoft OSS project. Microsoft should not add a Microsoft copyright header to third party contributions to Microsoft OSS projects. We should never remove copyright notices from files.

We should only add Microsoft copyright headers to files coded by Microsoft employees. If Microsoft employees modify third party code they may (but are not required to) add a Microsoft copyright header to the file so long as we keep intact all pre-existing copyright notices in the file.

Acceptance Criteria

• All files have the two lines of copyright code text above as a comment.

[brooke-hamilton]

@glennmusa, @Breanna-Stryker, @Phydeauxman, @kyle-hoyer
FYI on this issue as we work on code in this repo.