cli: Rename frontend plugin templates and add auto-detection

Renamed the CLI templates for frontend plugins:
- new-frontend-plugin → frontend-plugin
- new-frontend-plugin-module → frontend-plugin-module
- frontend-plugin (legacy) → legacy-frontend-plugin

Added auto-detection logic that checks packages/app/package.json to
determine which frontend system the app uses. When using default
templates, only the appropriate frontend plugin template is shown:
- Apps with @backstage/frontend-defaults see the new system templates
- Apps with @backstage/app-defaults see the legacy template

Both templates display as "frontend-plugin" to users, so existing
workflows are preserved while automatically using the correct template.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

docs/tooling/cli/04-templates.md

@@ -83,6 +83,8 @@ When defining the `templates` array it will override the default set of template
       "new": {
         "templates": [
           "@backstage/cli-module-new/templates/frontend-plugin",
+          "@backstage/cli-module-new/templates/frontend-plugin-module",
+          "@backstage/cli-module-new/templates/legacy-frontend-plugin",
           "@backstage/cli-module-new/templates/backend-plugin",
           "@backstage/cli-module-new/templates/backend-plugin-module",
           "@backstage/cli-module-new/templates/plugin-web-library",
@@ -90,6 +92,7 @@ When defining the `templates` array it will override the default set of template
           "@backstage/cli-module-new/templates/plugin-common-library",
           "@backstage/cli-module-new/templates/web-library",
           "@backstage/cli-module-new/templates/node-library",
+          "@backstage/cli-module-new/templates/cli-module",
           "@backstage/cli-module-new/templates/catalog-provider-module",
           "@backstage/cli-module-new/templates/scaffolder-backend-module"
         ]