Migrate redirects from docs-site to docs-builder

[bmorelli25]

Summary

Redirects have broken.

Migrate to our redirect service:

• https://github.com/elastic/docs-site/blob/main/config/redirects/integrations.js
• https://github.com/elastic/docs-site/blob/main/config/redirects/search-ui.js
• https://github.com/elastic/docs-site/blob/main/config/redirects/serverless.js

[reakaleek]

• serverless https://github.com/elastic/docs-infra/pull/53
• integrations https://github.com/elastic/docs-infra/pull/51
• search-ui https://github.com/elastic/docs-infra/pull/55

Right now, we just did this as quick as possible.
In the future we might want to have redirect logic in docs-builder. We then upload the redirect logic during deployment.