Issue Description: 

Our current approach to validation has grown organically. This means the approach is fractured and not consistent. We better understand the requirements of how we want to approach validation, so now is a good time to stop, reflect on what we've learnt and converge on a single, future-proof approach to validation.

There are a few docs that contain some initial thoughts and requirements:

• https://docs.google.com/document/d/15MOIbWvwjIatbOzulXcbqRfBrYADi51AqLelNFmtT_8/edit#
• https://docs.google.com/document/d/16U37Wv8UuCDBAJqQpuiDy7ttYJ-JMAl0GHp7wG6S6LE/edit
• https://docs.google.com/document/d/1PG7bBWple8VZw4P8G2j0acu_rxtFZTyfRq31_1Yze6w/edit#

Acceptance Criteria: 

• Create a single solution to how RHOSE handles validation failure at the API level
• Present the approach as an opportunity to standardise validation reporting across all MAS APIs
• Update test introduced as part of https://github.com/5733d9e2be6485d52ffa08870cabdee0/sandbox/pull/1066/files