[Lens] [ES|QL] Fixes inline documentation in cloud (elastic#177774)

## Summary

In the cloud distribution the documentation popovers are not rendered
correctly (ES|QL and Lens) This is because the documentation.scss file
is not loaded. This happens due to the sideEffects option.

This is happening only on production mode and not on dev mode.
You can use this a la carte instance for testing or create your own
https://stratoula-pr-177774-fix-documentation-in-cloud.kbndev.co/

### How to test
Open the ES|QL inline documentation or the Lens formula inline
documentation,

packages/kbn-language-documentation-popover/package.json

@@ -3,5 +3,7 @@
   "version": "1.0.0",
   "license": "SSPL-1.0 OR Elastic License 2.0",
   "private": true,
-  "sideEffects": false
+  "sideEffects": [
+    "*.scss"
+  ]
 }