Update immutable file list for CM/AMS

CSE from Adobe (Ranjith Radhakrishnan) said that:

> ams_default.vars is immutable. just validated with the CM specialist

However, it is not reflected in the build configuration e.g in 'https://github.com/adobe/aem-project-archetype/blob/develop/src/main/archetype/dispatcher.ams/immutable.files' nor https://github.com/adobe/aem-project-archetype/blob/develop/src/main/archetype/dispatcher.ams/pom.xml#L54 nor official documentation https://experienceleague.adobe.com/en/docs/experience-manager-learn/ams/dispatcher/immutable-files

### Expected Behaviour

as 'ams_default.vars' is immutable it should be configured in maven-enforcer-plugin

### Actual Behaviour

There is no info in the documentation (https://experienceleague.adobe.com/en/docs/experience-manager-learn/ams/dispatcher/immutable-files) nor the build is not complaining that the immutable file has been touched

my CM build (AMS enterprise / not AEMaaCS) broke because AMS deployment has overridden my file and because of missing vars that I appended there the HTTPD could not start.

### Side info

Please review the complete list of all immutable files and document them to avoid observing the unpredicted behavior on CM/AMS

Start by reviewing src/main/archetype/dispatcher.ams/immutable.files and the maven-enforcer-plugin configuration in src/main/archetype/dispatcher.ams/pom.xml, then compare both with the official immutable-files documentation. Confirm the complete immutable-file list, including ams_default.vars, is consistently configured and documented, and verify that touching an immutable file causes the build to complain.

Written by the indexing model from the issue text.