Remove joi leakage to the browser in @kbn/search-connectors

[afharo]

Summary

When working on #186547, I noticed that some bundle sizes were affected... This PR removes leaking point of joi to the browser 😇

For maintainers

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

[afharo]

/ci

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 29cd6b8

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
enterpriseSearch	2337	2274	-63
serverlessSearch	346	281	-65
total			-128

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
enterpriseSearch	2.7MB	2.5MB	-190.1KB
serverlessSearch	513.4KB	320.7KB	-192.8KB
total			-382.9KB

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

cc @afharo