docs: align discovery examples with ucp schema

[gil--]

Description

Align discovery examples with UCP schema

• wrap extension/service discovery examples with ucp
• add spec/schema/extends where required
• fix invalid JSON commas in REST examples

Type of change

• Documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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