Add JSON Schema Definition for gen_ai.tool.definitions

[Cirilla-zmh]

Fixes #2721 #1835

Changes

Add JSON schema definition for gen_ai.tool.definitions.

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Merge requirement checklist

• [x] CONTRIBUTING.md guidelines followed.
• [x] Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• [x] Links to the prototypes or existing instrumentations (when adding or changing conventions)