Consolidate all usage of wiki ID within Meza

[freephile]

In LocalSettings.php (and other PHP code generated by Meza), the wiki identifier variable name is $wikiId. In CLI scripts and the shell environment, the variable default name is WIKI. In YAML files or Ansible commands, the variable name is wiki_id. Why are there three different names for the same thing? This difference no doubt causes some confusion, while respecting traditional naming conventions in PHP, BASH and YAML. Convention could be ignored to use a consistent variable name e.g. WIKI_ID or SITE_ID throughout.

Variable Name	Language
$wikiId	PHP
WIKI	BASH
wiki_id	YAML
SITE_ID	proposed

[freephile]

I referred to this in documentation https://www.mediawiki.org/wiki/Meza/Commands#MediaWiki_Maintenance to help new users not get confused by 3 different names for the same thing.