Grafana UI: Expose unstable entrypoint (#97080)

* feat(grafana-ui): build unstable entrypoint for experimental components

* feat(plugins): expose grafana/ui/unstable

* build(grafana-ui): add rollup plugin to create alias package.json for unstable entrypoint

* build(packages): rewrite prepare npm script to generate alias packagejson files

* chore(packages): use relative paths in publishConfig for exports generation

* chore(frontend): move npmcli/package-json package to root package.json

* revert(grafana-ui): remove rollup plugin for generating alias package.json files

* chore(grafana-ui): clean up unstable directory postpack to prevent yarn lock issues

* build(packages): fix scope for pkgName usage

* feat(packages): create separate cjs and esm builds that validate with arethetypeswrong cli

* chore(yarn): refresh lock file

* fix(packages): make sure alias package.jsons point to existing files

package.json

@@ -83,6 +83,7 @@
     "@grafana/plugin-e2e": "1.17.1",
     "@grafana/tsconfig": "^2.0.0",
     "@manypkg/get-packages": "^2.2.0",
+    "@npmcli/package-json": "^5.2.0",
     "@playwright/test": "1.50.1",
     "@pmmmwh/react-refresh-webpack-plugin": "0.5.15",
     "@react-types/button": "3.10.2",