[Validator] added a deprecation note about MetadataFactoryInterface addressing #12690
minor #12753 [Validator] added a deprecation note about MetadataFactoryInterface (Ismail Faizi)

This PR was merged into the 2.7 branch.

Discussion
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[Validator] added a deprecation note about MetadataFactoryInterface

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12690
| License       | MIT
| Doc PR        |

Commits
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33fa8ff [Validator] added a deprecation note about MetadataFactoryInterface addressing #12690