Fix documentation of ECS fields in linked files

[jsoriano]

Fields validator is used for many things, including looking for fields for documentation.
In any case, it needs to resolve linked fields files, so the fields the linked files contain are included in documentation, built packages and validation processes.
This change explicitly includes links resolution in the validator, what makes it depend on a repository root. Most of the changes here are related to passing the repository root to the validator.

[elasticmachine]

💔 Build Failed

• Buildkite Build
• Commit: 5ab7ad2

Failed CI Steps

• :go: Integration test (false positive): httpjson_false_positive_asserts

History

• 💔 Build #6767 failed 17c2057
• 💔 Build #6766 failed 63c4f71
• 💔 Build #6764 failed 7ea1d98
• 💔 Build #6688 failed 99fc576

[jsoriano]

test integrations

[elastic-vault-github-plugin-prod]

Created or updated PR in integrations repository to test this version. Check elastic/integrations#16238