feat: install most dependencies in cacheable layer, before adding main

Instead of requiring the whole stack to be reinstalled whenever a specific version (e.g. main) causes a cache fail, this aims to have stable default version with a second-stage installation of the potentially-modified versions of eicrecon and juggler. This should allow all builds to cache the first installation in virtually all cases, leading to faster builds.

.gitlab-ci.yml

@@ -7,7 +7,7 @@ variables:
 
   ## Application versions used for the main release 
   ## note: nightly builds will always use the master/main branch
-  JUGGLER_VERSION: "v11.0.0"
+  JUGGLER_VERSION: "v12.0.0"
   EICRECON_VERSION: "v1.9.0"
 
   ## Local registry