add trigger message
minor #12763 [Validator] [Deprecated] Add a deprecation note about ElementMetadata (davidromani)

This PR was merged into the 2.7 branch.

Discussion
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[Validator] [Deprecated] Add a deprecation note about ElementMetadata

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #12682
| License       | MIT
| Doc PR        |

Commits
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21c32b5 add trigger message