[BUG] channelName variable is not available in Postprocessor script

[xabylr]

Describe the bug
The channelName variable is not available in the Postprocessor script. It makes no sense that is not available, since it is available for the Deploy, Undeploy and Preprocessor scripts.

To Reproduce

1. Create a channel with a Postprocessor script that makes use of the channelName variable.
2. Send a message to the channel and observe that the variable does not exist.

Expected behavior
The variable channelName should be available in the Postprocessor script.

Actual behavior
The variable channelName is not available in the Postprocessor script.

Screenshots

Environment:

• Docker image: 4.5.2-ubuntu
• OS: Linux
• Java Distribution/Version: OpenJDK 17
• Connect Version: 4.5.2

Workaround(s)
Obtain the channel name in other place that where is available and store it in another variable that the Postprocessor script has access to.

Additional context
There was already a bug report for Mirth Connect, but it was automatically closed without a fix: nextgenhealthcare/connect#3893