Add: allow setting the highest mountain for heightmaps

It will add some slack to the map height limit if that was set
to auto.

src/table/settings.ini

@@ -405,6 +405,17 @@ strval   = STR_CONFIG_SETTING_MAP_HEIGHT_LIMIT_VALUE
 proc     = ChangeMaxHeightLevel
 cat      = SC_ADVANCED
 
+[SDT_VAR]
+base     = GameSettings
+var      = game_creation.heightmap_height
+type     = SLE_UINT8
+flags    = SLF_NOT_IN_SAVE | SLF_NO_NETWORK_SYNC
+guiflags = SGF_NEWGAME_ONLY
+def      = MAP_HEIGHT_LIMIT_AUTO_MINIMUM
+min      = MIN_HEIGHTMAP_HEIGHT
+max      = MAX_MAP_HEIGHT_LIMIT
+interval = 1
+
 [SDT_BOOL]
 base     = GameSettings
 var      = construction.build_on_slopes