Playwright: Gate server start up with GRAFANA_URL env var (#108302)

* refactor so server is created unless GRAFANA_URL is provided

* update documentation

* don't swallow errors from the server process

package.json

@@ -24,7 +24,6 @@
     "e2e:enterprise:dev": "./e2e/start-and-run-suite enterprise dev",
     "e2e:enterprise:debug": "./e2e/start-and-run-suite enterprise debug",
     "e2e:playwright": "yarn playwright test",
-    "e2e:playwright:server": "yarn e2e:plugin:build && ./e2e-playwright/start-and-run-suite",
     "e2e:playwright:storybook": "yarn playwright test -c playwright.storybook.config.ts",
     "e2e:storybook": "PORT=9001 ./e2e/run-suite storybook true",
     "e2e:plugin:build": "nx run-many -t build --projects='@test-plugins/*'",