Add User Input variable for channel point event

[bizzycola]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Problem/Feature

Fixes the inability to supply the user input field for the channel point redemption event.

Description of Changes:

Adds a --user-input flag for the channel point redemption event to test with specific user prompts.

Checklist

• [ x] My code follows the Contribution Guide
• [ x] I have self-reviewed the changes being requested
• [ x] I have made comments on pieces of code that may be difficult to understand for other editors
• [ x] I have updated the documentation (if applicable)

[bizzycola]

The only comment I have here for an uncertainty is what to do if no input is supplied.

To prevent breaking anything, it seems the best idea would be to check for an empty string and just set the user input to the original test value. However, I also need the ability to test when a user sends an empty string.

Suggestions welcome.