Draft: Resolve "Create GraphQL mutations for pages settings"

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What does this MR do and why?

Create GraphQL mutations for setting pagesForceHttps and pagesUseUniqueDomain

References

MR acceptance checklist

• For each mutation there should be a new file in app/graphql/mutations/pages that implements the mutation.

• The mutation classes then need to be added to app/graphql/types/mutation_type.rb to make them available.

• There should be a unit test for each mutation in spec/graphql/mutations/pages/.

Screenshots or screen recordings

How to set up and validate locally

Related to #469039 (closed)