Add a note about disabling Apollo Client cache when used in Vuex

What does this MR do?

As described in #198624 (closed), we disable an Apollo cache when Apollo is used with Vuex to prevent storing data twice. This MR adds a note about this to our Frontend GraphQL guide.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #199398 (closed)