Improve the optional unit handling in layouts

added the fill property to the layout groups which allows to specify if a optional layout group should be filled with a faction accessible unit if it was not defined by the preset groups. This is usefull to allow more generalized templates which for example may or may not have a Search Radar without adding one to all layouts (example: Rapier and Roland Sites which use the generic SHORAD layout)

this fixes an issue which prevented optional units like logistics to be added to the forcegroup if they were not defined in the preset group yaml

resources/layouts/anti_air/4_Launcher_Site.yaml

@@ -12,12 +12,14 @@ groups:
         - SearchTrackRadar
     - name: Track Radar
       optional: true # Allow groups without TR
+      fill: false # Do not fill with faction possible units
       unit_count:
         - 1
       unit_classes:
         - TrackRadar
     - name: Command Post
       optional: true
+      fill: false # Do not fill with faction possible units
       unit_count:
         - 1
       unit_classes:

resources/layouts/anti_air/6_Launcher_Site.yaml

@@ -12,17 +12,18 @@ groups:
         - SearchTrackRadar
     - name: Track Radar
       optional: true # Allow groups without TR
+      fill: false # Do not fill with faction possible units
       unit_count:
         - 1
       unit_classes:
         - TrackRadar
     - name: Command Post
       optional: true
+      fill: false # Do not fill with faction possible units
       unit_count:
         - 1
       unit_classes:
         - CommandPost
-    
     - name: Launcher
       unit_count:
         - 6

resources/layouts/anti_air/Cold_War_Flak_Site.yaml

@@ -3,8 +3,9 @@ tasks:
   - AAA
 groups:
   - AAA:
-    - name: Cold War Flak Site Radar
+    - name: Cold War Flak Site Radar 
       optional: true # Only available to Late Cold War
+      fill: false # Do not fill with faction possible units
       unit_count:
         - 1
       unit_classes:

resources/layouts/anti_air/SHORAD_TR.yaml

@@ -5,6 +5,7 @@ groups:
   - SHORAD:
     - name: SHORAD STR
       optional: true
+      fill: false # Do not fill with faction possible units
       unit_count:
         - 1
       unit_classes:
@@ -13,6 +14,7 @@ groups:
         - TrackRadar
     - name: SHORAD OTR
       optional: true
+      fill: false # Do not fill with faction possible units
       unit_count:
         - 1
       unit_classes: