[#75] Fix: set default value for role in public Content class and builder

[PatilShreyas]

Summary

• Specify default value for role as a "user" in a public API class Content.
• Added tests for the verification of conversion functions (from public class to internal class and vice versa).

Fixes: #75

[rlazo]

Hey @PatilShreyas thanks for your contribution. I only have one outstanding comment, which is to include the copyright notice in the header of the test file. Once that's in I'll be able to merge your change. Thanks!

[PatilShreyas]

Hey @PatilShreyas thanks for your contribution. I only have one outstanding comment, which is to include the copyright notice in the header of the test file. Once that's in I'll be able to merge your change. Thanks!

Done. I thought it'd be applied automatically when I ran the ktfmtFormat gradle task. I just got to know about the applyLicense gradle task. Thanks!