Replace GraphQL error string with constant

What does this MR do and why?

replaces GraphQL error string to reference a constant to reduce maintenance burden to keep these in sync.

Output

[4] pry(main)> Gitlab::Graphql::Authorize::AuthorizeResource::RESOURCE_ACCESS_ERROR == "The resource that you are attempting to access does not exist or you don't have permission to perform this action"
=> true

MR acceptance checklist

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