Move @backstage/backend-defaults to devDependencies in backend plugins

Move @backstage/backend-defaults from dependencies to devDependencies
in all backend plugins that had it as a production dependency. None of
these plugins use it in their production source code - it's only needed
for dev servers (dev/index.ts) and test files.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

plugins/techdocs-backend/package.json

@@ -61,7 +61,6 @@
     "test": "backstage-cli package test"
   },
   "dependencies": {
-    "@backstage/backend-defaults": "workspace:^",
     "@backstage/backend-plugin-api": "workspace:^",
     "@backstage/catalog-client": "workspace:^",
     "@backstage/catalog-model": "workspace:^",