[WIP] Flag @kbn/config-schema as server-only

[afharo]

Summary

After #188606, let's enforce @kbn/config-schema to be a shared-server to ensure that it never leaks to the browser anymore.

To make reviews easier, I'll apply the fixes in separate PRs, and keep rebasing this one until the CI is green. Not setting it as draft to avoid having to comment /ci on every push. Reviewers, feel free to unsubscribe from the notifications. I'll ping you once it's all ready.

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[afharo]

/ci

[kibana-ci]

💔 Build Failed

• Buildkite Build
• Commit: 2cb4cb7
• Interpreting CI Failures

Failed CI Steps

• Linting

Metrics [docs]

✅ unchanged

History

• 💔 Build #230955 failed 0e21ee6
• 💔 Build #230870 failed 45d3b57
• 💔 Build #230509 failed 703568e
• 💔 Build #230161 failed 853f8fc
• 💔 Build #226924 failed 4873aa9

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @afharo