Improve HAML to JS bootstrapping docs

What does this MR do?

This MR updates the Bootstrapping Gotchas documentation for Providing data from HAML to JavaScript https://docs.gitlab.com/ee///development/fe_guide/vue.html#providing-data-from-haml-to-javascript

It borrows some information from https://docs.gitlab.com/ee/development/fe_guide/vuex.html#why-not-just-spread-the-initial-state and places a similar example in this area of our docs

Screenshots

fe_guide/style/vue.html

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fe_guide/vue.html

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fe_guide/vuex.html

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Next steps

Once this is merged, I'll announce the docs update on all of the relevant channels and open an epic with issues to fix existing occurrences of this.