Commonize License In Every File

[zromano]

We have a license at the top of every file, but they are not the same in every file.

Acceptance Criteria:

• Make the license at the top of every file consistent
• Add a test in the pipeline that asserts that every *.java file in our repo starts with that same license

[zromano]

Done in https://github.com/smartsheet/smartsheet-java-sdk/pull/63