[Feature Request]: Validate redirects.yml inputs

[reakaleek]

Prerequisites

• I have searched existing issues to ensure this feature hasn't already been requested
• I have tested using the latest version of docs-builder

What problem are you trying to solve?

When you redirect to a path without .md extension, you get unexpected results in during cross-link validation.

The configuration in apm-agent-android causes this error during an assembler build.

error::d.a.b.AssemblerBuilder:: An error occurred while resolving cross-link opentelemetry://reference/edot-sdks/android: 'reference/edot-sdks/android' is not a valid link in the 'opentelemetry' cross link index: https://elastic-docs-link-index.s3.us-east-2.amazonaws.com/elastic/opentelemetry/main/links.json
error::d.a.b.AssemblerBuilder:: An error occurred while resolving cross-link opentelemetry://reference/edot-sdks/android/getting-started: 'reference/edot-sdks/android/getting-started' is not a valid link in the 'opentelemetry' cross link index: https://elastic-docs-link-index.s3.us-east-2.amazonaws.com/elastic/opentelemetry/main/links.json
error::d.a.b.AssemblerBuilder:: An error occurred while resolving cross-link opentelemetry://reference/edot-sdks/android/troubleshooting: 'reference/edot-sdks/android/troubleshooting' is not a valid link in the 'opentelemetry' cross link index: https://elastic-docs-link-index.s3.us-east-2.amazonaws.com/elastic/opentelemetry/main/links.json

Proposed Solution

Validate the redirects.yml file and it's values.

Examples and Research

No response

Alternative Solutions

No response

Additional Context

No response

How important is this feature to you?

Nice to have

[reakaleek]

This PR should fix the error.

[cotti]

Linting rules:

• Paths should not be absolute (/reference/... -> reference/...)
• Redirect rule keys (from) should not reference a different repository (other-repo://reference/... -> reference/...)
• Redirect rules must be from file to file (path/to/doc -> path/to/doc.md)

[bmorelli25]

Is this done?