feat: add GHES 3.11, GHES 3.12, remove GHES 3.7, many description updates and new enpoints (#395)

* new DELETE method for `/notifications/threads/{thread_id}` endpoint,
* new organization-roles endpoints
* new `/repos/{owner}/{repo}/pages/deployments/{pages_deployment_id}`
* `/repos/{owner}/{repo}/pages/deployments/{pages_deployment_id}/cancel` endpoints
* new PATCH method for `/repos/{owner}/{repo}/properties/values`
* new `/repos/{owner}/{repo}/security-advisories/{ghsa_id}/forks` endpoint

BREAKING CHANGE: Drop GHES 3.7

Author: octokitbot