feat(rulesets): add oas3_1-servers-in-webhook and oas3_1-callbacks-in…

[kaylachun]

…-webhook rules

Fixes #[ISSUE_NUMBER].

Checklist

• [x] Tests added / updated
• [x] Docs added / updated

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

If indicated yes above, please describe the breaking change(s).

Remove this quote before creating the PR.

Screenshots

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Additional context

Added two new spectral rules:

• oas3_1-servers-in-webhook
  • warns if servers is defined in a webhook
• oas3_1-callbacks-in-webhook
  • warns if callbacks is defined in webhook operation

[stoplight-bot]

:tada: This PR is included in version 1.19.0 :tada:

The release is available on @stoplight/spectral-rulesets-1.19.0

Your semantic-release bot :package::rocket: