fix: Request Validator incorrectly refers to Kong format schema

[lena-larionova]

Description

The doc says the the Kong format schema validation is supported, which is incorrect. JSON Schema format validation is actually what's supported.

Fixes https://konghq.atlassian.net/browse/FTI-6196.

Note to reviewers: I fixed the title of the section referring to the "Kong format schema" and some minor cleanup to the page, including removing unnecessary output examples.
However, I couldn't actually get these examples to work as documented in the example. The last step, validation, always fails for me- though this is probably out of scope of this PR and is a separate issue.

Testing instructions

Preview link:

Checklist

• Review label added
• Conditional version tags added, if applicable.

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