this makes it easier to use `PublishWithDeferredConfirmWithContext`
without generating a custom handler that does nothing.
Add an additional example for this that also shows how to use
PublishWithDeferredConfirmWithContext.
Closes: https://github.com/wagslane/go-rabbitmq/issues/116
- 'Publish' has been deprecared by rabbitmq/ampq091-go.
- 'PublishWithContext' has been introduced to pass context
while publishing for cancellation.
- Update examples to use PublishWithContext.
Signed-off-by: Aaqa Ishtyaq <aaqa@hackerrank.com>