DRY up workspace_agent_config models validators

MR: Pending

Description

Context - !186027 (comment 2419088995)

Acceptance criteria

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• [Describe what must be achieved to complete this issue.]
• [If applicable, please provide design specifications for this feature/enhancement.]
• [If applicable, please list any technical requirements (performance, security, database, etc.)]

Implementation plan

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[Provide a high-level plan for implementation of this issue, including relevant technical and/or design details.]