feat(config): enable reuse of mfm configuration variables

This change introduces a two-pass parsing approach to allow reuse of mfm
configuration variables within other configuration parts. This initial
implementation does not handle recursive dependencies, which is
acceptable for the current requirements.

- Implemented a two-pass parsing mechanism for configuration files.
- Added mfm configuration variables to the Crinja render context in both
  passes.
- Ensured the global mount point base is safely retrieved and validated
  in each pass.

Signed-off-by: Glenn Y. Rolland <glenux@glenux.net>

src/config.cr

@@ -94,14 +94,37 @@ module GX
         exit(1)
       end
 
+      ## PASS 1
       file_data = File.read(config_path)
-      file_patched = Crinja.render(file_data, {"env" => ENV.to_h})
+      file_patched = Crinja.render(
-
+        file_data, 
+        {
+          "env" => ENV.to_h, 
+          "mfm" => {
+            "global" => {"mount_point_base" => "" }
+          }
+        }
+      )
       root = Models::RootConfig.from_yaml(file_patched)
 
       mount_point_base_safe = root.global.mount_point_base
       raise Models::InvalidMountpointError.new("Invalid global mount point") if mount_point_base_safe.nil?
 
+      ## PASS 2
+      file_patched = Crinja.render(
+        file_data, 
+        {
+          "env" => ENV.to_h, 
+          "mfm" => {
+            "global" => {"mount_point_base" => mount_point_base_safe }
+          }
+        }
+      )
+
+      root = Models::RootConfig.from_yaml(file_patched)
+      mount_point_base_safe = root.global.mount_point_base
+      raise Models::InvalidMountpointError.new("Invalid global mount point") if mount_point_base_safe.nil?
+
       root.filesystems.each do |selected_filesystem|
         if !selected_filesystem.mount_point?
           selected_filesystem.mount_point =