Allow to generate old version of manifest / channel

[TomasHofman]

Either allow to specify desired schema version or perhaps generate the oldest possible? Or eventually implement operations to convert to older schema version.

We get exceptions from tooling that are not able to process the new schema versions...

[ERROR] Failed to execute goal org.wildfly.plugins:wildfly-maven-plugin:4.1.0.Final:provision (server-provisioning) on project wildfly-build: Execution server-provisioning of goal org.wildfly.plugins:wildfly-maven-plugin:4.1.0.Final:provision failed: Invalid Manifest
[ERROR] caused by:
[ERROR]  Unknown schema version "1.1.0"