Add RealTimeText to sample

[edwardlee-msft]

Purpose

• Add RealTimeText sample to the app
• Backwards compatible as it checks to see if the feature is available first before actioning or showing buttons
• Added small fix to CallCaptions to the PR as well as caption language was not being set correctly

Showcasing label

Showcasing Feature

Showcasing banner warning when trying to close/hide rtt

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[o] Bugfix
[o] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe: