Accessibility checks: Phase 2 - Adding Pa11y CI PR stage (#38556)

Co-authored-by: Hugo Häggmark <hugo.haggmark@grafana.com>

package.json

@@ -14,6 +14,8 @@
     "e2e:dev": "./e2e/start-and-run-suite dev",
     "test": "jest --notify --watch",
     "test:accessibility": "pa11y-ci --config .pa11yci.conf.js",
+    "test:accessibility-pr": "pa11y-ci --config .pa11yci-pr.conf.js",
+    "test:accessibility-report": "./scripts/generate-a11y-report.sh",
     "lint": "yarn run lint:ts && yarn run lint:sass",
     "lint:ts": "eslint . --ext .js,.tsx,.ts --cache",
     "lint:sass": "yarn run sass-lint -c public/sass/.sass-lint.yml 'public/sass/**/*.scss, packages/**/*.scss' -v -i '**/node_modules/**/*.scss'",
@@ -171,6 +173,7 @@
     "fs-extra": "9.1.0",
     "gaze": "1.1.3",
     "glob": "7.1.6",
+    "http-server": "13.0.1",
     "html-loader": "2.1.2",
     "html-webpack-harddisk-plugin": "2.0.0",
     "html-webpack-plugin": "5.3.2",