Add support for Kibana link checking

[bmorelli25]

Summary

We must ensure that links from Kibana (in the product) to documentation are valid. Our legacy doc build does this as a part of every documentation build. The relevant code is here: https://github.com/dedemorton/docs/blob/3546cbd00f03ef020248fba3ec33dda268c982b5/build_docs.pl#L230.

We can either solve this problem in the same way, or have a separate check that ensures links from Kibana are correct. This is the file that defines links in the Kibana repo:
https://github.com/elastic/kibana/blob/2b9104c3278e1684c31b8ffd623a428b178238c0/src/platform/packages/shared/kbn-doc-links/src/get_doc_links.ts

[lcawl]

These are the places that I'm currently aware of that have lists of documentation links:

• Kibana doc link service https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-doc-links/src/get_doc_links.ts

• Elasticsearch client and dev console links derived from https://github.com/elastic/elasticsearch-specification/blob/main/specification/_doc_ids/table.csv

• Cloud UI links https://github.com/elastic/cloud/tree/master/cloud-ui/apps/monolith/public/components/DocLink, https://github.com/elastic/cloud/blob/master/cloud-ui/apps/monolith/public/constants/docLinks.ts

• Elasticsearch error/log links: https://github.com/elastic/elasticsearch/blob/main/server/src/main/resources/org/elasticsearch/common/reference-docs-links.txt

As noted in #736 I think if we do implement link-checking for those URLs, we'll also need to ensure that all-supported branches/versions of those products have their links tested, so that we don't break older versions until they go out of service.