Adds documentation to use Vuex

What does this MR do?

Adds topics to help developers including Vuex and bootstraping a Vue application:

• How to provide initial data in a vue application
• How to get data from gl object
• How to include Vuex
• How to separate concerns (actions, getters, mutations, mutation types) and link to vuex docs
• How and why to use mutation types
• File structure of the store should look like (as stated in vuex docs)
• How to write tests for Vuex
• How to write tests for Vue components that use a Vuex Store
• How to include SVGs in .vue components

Does this MR meet the acceptance criteria?

• [ ] Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] API support added
• [ ] Tests added for this feature/bug
• Review
  • [ ] Has been reviewed by UX
  • Has been reviewed by Frontend
  • [ ] Has been reviewed by Backend
  • [ ] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #36070 (closed)