Change extension category (#749)

* Remove 'Extension Packs' category
to change its rendering in VS Code Extension Manager.
* Use .png variants of QLTY badges

---------

Signed-off-by: Jens Reinecke <jens.reinecke@arm.com>

Author: jreineckearm

README.md

@@ -1,5 +1,5 @@
-[![Maintainability](https://qlty.sh/badges/2170b449-4b4b-43e8-8bba-18665ed21a08/maintainability.svg)](https://qlty.sh/gh/Open-CMSIS-Pack/projects/vscode-cmsis-debugger)
-[![Test Coverage](https://qlty.sh/badges/2170b449-4b4b-43e8-8bba-18665ed21a08/coverage.svg)](https://qlty.sh/gh/Open-CMSIS-Pack/projects/vscode-cmsis-debugger)
+[![Maintainability](https://qlty.sh/badges/2170b449-4b4b-43e8-8bba-18665ed21a08/maintainability.png)](https://qlty.sh/gh/Open-CMSIS-Pack/projects/vscode-cmsis-debugger)
+[![Test Coverage](https://qlty.sh/badges/2170b449-4b4b-43e8-8bba-18665ed21a08/coverage.png)](https://qlty.sh/gh/Open-CMSIS-Pack/projects/vscode-cmsis-debugger)
 [![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/Open-CMSIS-Pack/vscode-cmsis-debugger/badge)](https://securityscorecards.dev/viewer/?uri=github.com/Open-CMSIS-Pack/vscode-cmsis-debugger)
 
 # Arm CMSIS Debugger

package.json

@@ -24,8 +24,7 @@
     "vscode": "^1.106.1"
   },
   "categories": [
-    "Debuggers",
-    "Extension Packs"
+    "Debuggers"
   ],
   "keywords": [
     "arm",