Dashboards: Fix text panel content loss during v1 to v2 migration (#115496)

* move content and mode properties to options level

* move to angular section

* Update comments

* handle missing angular text panel

* re-generate test files

* angualr panels tests

* fixing test

* Update output files

* Update output for dev dashboard

* Spread options at the top panel level for migration

* linting issue

---------

Co-authored-by: Ivan Ortega <ivanortegaalba@gmail.com>

apps/dashboard/pkg/migration/conversion/testdata/input/migrated_dev_dashboards/migrations/v0alpha1.migrations.v42.json

@@ -300,15 +300,9 @@
         "y": 0
       },
       "id": 6,
-      "options": {
-        "code": {
-          "language": "plaintext",
-          "showLineNumbers": false,
-          "showMiniMap": false
-        },
-        "content": "# Graph panel \u003e\u003e Timeseries panel\n\nKnown issues:\n* hiding null/empty series\n* time regions",
-        "mode": "markdown"
-      },
+      "options": {},
+      "content": "# Graph panel \u003e\u003e Timeseries panel\n\nKnown issues:\n* hiding null/empty series\n* time regions",
+      "mode": "markdown",
       "pluginVersion": "11.0.0-pre",
       "targets": [
         {