docs(QueryStatus): change from enum to union type

[luisadame]

Description

In version 2 the QueryStatus typing was:

export enum QueryStatus {
  Idle = 'idle',
  Loading = 'loading',
  Error = 'error',
  Success = 'success',
}

https://github.com/tannerlinsley/react-query/blame/8aeb209c3b9c84382a88059afbc398be93a69b33/src/core/types.ts#L183

And now in version 3 is:

export type QueryStatus = 'idle' | 'loading' | 'error' | 'success'

https://github.com/tannerlinsley/react-query/blame/7b14ef519a544d725f2cff99574f0a01f92b8c94/src/core/types.ts#L257

Changes

• documented the change described above
• added underline to links that are children of headings
  
  
  this affects anchor links but these already have an underline property set, so I think there's no issue with that

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[tannerlinsley]

🎉 This PR is included in version 3.13.5 🎉

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