Fix Fields search options leaking across entity scopes

[brunoCarraroGridtech]

Checklist before requesting a review

Please delete options that are not relevant.

• [X ] I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• [X ] This change requires a documentation update.

Description

• It fixes # (issue number, if applicable)
• Adds Entity and Child entities settings to Fields containers, allowing each additional-fields block to be scoped to a specific GLPI entity. It also makes Fields search and filter options respect that same entity scope, preventing client-specific fields from appearing in unrelated entities.

Screenshots (if appropriate):