Release note pages 404 in staging

[bmorelli25]

Summary

In staging, some release note pages are 404ing. @colleenmcginnis pointed out that it appears to be all of the pages that live in docs-content.

Steps to repro

1. Head to https://staging-website.elastic.co/docs/release-notes
2. Click on any of the following: Elastic Observability, Elastic Security, Fleet and Elastic Agent
3. See 404

[bmorelli25]

@colleenmcginnis spotted the problem: there's no index.md file in these directories. For example: https://github.com/elastic/docs-content/tree/main/release-notes/elastic-observability

We should update our build to error in this situation.

[bmorelli25]

Interestingly enough, Elastic Cloud Serverless also 404s, but it gets closest to working. Clicking on the release note page brings you to: https://staging-website.elastic.co/docs/release-notes/cloud-serverless/hangelog. Notice the missing "c" from the beginning of "hangelog"

@cotti could this be the same TrimStart() error seen/fixed in #835?

[cotti]

Interestingly enough, Elastic Cloud Serverless also 404s, but it gets closest to working. Clicking on the release note page brings you to: https://staging-website.elastic.co/docs/release-notes/cloud-serverless/hangelog. Notice the missing "c" from the beginning of "hangelog"

@cotti could this be the same TrimStart() error seen/fixed in #835?

It is! Just found some other weird URLs, such as "docs/release-notes/cloud-serverless/precations" (should be deprecations). I'll prep a fix for this now.