Fix geosolutions-it#11794 Update the configuration and migration guide for map viewer (geosolutions-it#11968)

* Update the configuration and migration guide for map viewer
* Fix the migration guide lint issue

Author: subashtiwari1010

docs/developer-guide/mapstore-migration-guide.md

@@ -108,6 +108,71 @@ As part of extending the functionalities of the CRS selector, we have deprecated
 }
 ```
 
+### Update containerPosition for the Map and FeatureEditor plugin
+
+The `Map` and `FeatureEditor` plugins require explicit `containerPosition` configuration for proper layout placement. The `Map` plugin renders the map as a background layer, while `FeatureEditor` displays the feature grid in a bottom panel.
+
+**localConfig.json** — Add `containerPosition` to the plugin `cfg` in the `desktop` (and optionally `mobile`/`embedded`) plugins array:
+
+```diff
+{
+    "plugins": {
+        "desktop": [
+            ...,
+            {
+                "name": "Map",
+                "cfg": {
++                    "containerPosition": "background",
+                    "mapOptions": { ... },
+                    "toolsOptions": { ... }
+                }
+            },
+            ...
+            {
+                "name": "FeatureEditor",
++                "cfg": {
++                    "containerPosition": "bottom"
++                }
+            },
+            ...
+        ]
+    }
+}
+```
+
+**pluginsConfig.json** — Add `containerPosition` inside `defaultConfig` for each plugin:
+
+```diff
+{
+    "plugins": [
+        {
+            "name": "Map",
+            "mandatory": true,
+            "defaultConfig": {
+                "mapOptions": { ... },
+                "toolsOptions": { ... },
++                "containerPosition": "background"
+            }
+        },
+        ...
+        {
+            "name": "FeatureEditor",
+            "defaultConfig": {
++                "containerPosition": "bottom"
+            }
+        },
+        ...
+    ]
+}
+```
+
+**Reference values:**
+
+| Plugin        | containerPosition | Purpose                                       |
+|---------------|-------------------|-----------------------------------------------|
+| Map           | `"background"`    | Renders the map as the main background layer  |
+| FeatureEditor | `"bottom"`        | Shows the feature grid in a bottom panel      |
+
 ## Migration from 2025.01.01 to 2025.02.00
 
 ### Update authenticationRules in localConfig.json

web/client/configs/pluginsConfig.json

@@ -25,7 +25,8 @@
           "scalebar": {
             "container": "#footer-scalebar-container"
           }
-        }
+        },
+        "containerPosition": "background"
       }
     },
     {
@@ -82,7 +83,9 @@
       "dependencies": ["QueryPanel"],
       "children": ["LayerDownload"],
       "autoEnableChildren": ["LayerDownload"],
-      "defaultConfig": {}
+      "defaultConfig": {
+        "containerPosition": "bottom"
+      }
     },
     {
       "name": "TOCItemsSettings",