The mod_proxy configuration is not compatible with current AMS

The generated vhost files for author and publisher includes a block that's using a directive (SSLProxyEngine) not available in Apache 2.4.6 that's deployed on standard AMS.
```
AH00526: Syntax error on line 66 of /etc/httpd/conf.d/enabled_vhosts/aem_author.vhost:
Invalid command 'SSLProxyEngine', perhaps misspelled or defined by a module not included in the server configuration
```
This directive appears to only be available in Apache 2.4.30+

Furthermore, the proxy directory missing if the commerce module is not enabled, resulting in a startup failure.
```
httpd: Syntax error on line 353 of /etc/httpd/conf/httpd.conf: Syntax error on line 35 of /etc/httpd/conf.d/dispatcher_vhost.conf: Syntax error on line 67 of /etc/httpd/conf.d/enabled_vhosts/aem_author.vhost: Could not open config directory /etc/httpd/conf.d/proxy: No such file or directory
```
and if the directory is created, startup still fails due to the use of Include instead of IncludeOptional
```
httpd: Syntax error on line 353 of /etc/httpd/conf/httpd.conf: Syntax error on line 35 of /etc/httpd/conf.d/dispatcher_vhost.conf: Syntax error on line 67 of /etc/httpd/conf.d/enabled_vhosts/aem_author.vhost: No matches for the wildcard '*.proxy' in '/etc/httpd/conf.d/proxy', failing (use IncludeOptional if required)
```

https://github.com/adobe/aem-project-archetype/blob/33ccc1fefddee72f6b2b94ab3f1d73c9b2fc7108/src/main/archetype/dispatcher.ams/src/conf.d/available_vhosts/__appId___publish.vhost#L60
https://github.com/adobe/aem-project-archetype/blob/33ccc1fefddee72f6b2b94ab3f1d73c9b2fc7108/src/main/archetype/dispatcher.ams/src/conf.d/available_vhosts/aem_author.vhost#L65

Start with the generated files at src/main/archetype/dispatcher.ams/src/conf.d/available_vhosts/__appId___publish.vhost and aem_author.vhost, especially the linked lines. Check how the SSLProxyEngine directive and proxy-directory Include are emitted when commerce is disabled, then validate the generated Apache configuration on the stated AMS version. Done means author and publisher vhosts start successfully in both commerce-enabled and disabled configurations.

Written by the indexing model from the issue text.