Update GraphQL query limit docs to include mutations

What does this MR do and why?

Describe in detail what your merge request does and why.

Through researching #390187 (closed) (Query too large error) we identified that our GraphQL docs highlight a limit for queries, but not mutations. This MR extends to include mutations for clarity.

Example showing limit enforced on a mutation, using GraphiQL. The solution, as directed by the docs, is to split out the data into an input parameter.

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