[DOC] - Add CXML Error Code 31922

[cassieemb]

Describe the requested update
We would like to add a new CXML error code mapping.

The code is 31922, and like its Twilio code reference, it is returned when an invalid stream URL is passed for calls or conferences.

In this case, invalid stream URL could mean:

• The URL schema is not WSS
• The URL has a trailing whitespace
• The URL has an embedded whitespace

Reason for the request
Previously, we were not detecting the invalid URL on the request to create the stream itself. Instead, it would "succeed", but then silently fail to start.

We added this new code and error to help our customers understand if something is invalid before the request is created instead of debugging after.

Sections to be updated
https://developer.signalwire.com/rest/compatibility-api/overview/error-codes

Additional context
Examples of the returned error:

Related Issues or PRs
https://github.com/signalwire/cloud-product/issues/16217

[Manny-r31]

addressed in #594 .