Roadmaps refactoring: move non-reactive properties from Vuex to inject

What does this MR do and why?

This MR is a part of refactoring roadmaps to use VueApollo effort. Here, before introducing VueApollo, we reduce the number of Vuex properties by moving a few of them to provide/inject.

Two of these properties, epicIid and fullPath are not removed from Vuex yet (this will be done in subsequent MRs) but added to provided properties because we will need them in the next MR as variables for GraphQL calls from the component.

MRs for Roadmaps refactoring

Title	Link
👉 Move non-reactive properties from Vuex to injected	!148520 (merged)
Move fetching child epics logic to epic_item.vue	TBD
Move fetching milestones logic	TBD
Move fetching group epics logic	TBD
Move filter params to root component property	TBD
Move local settings to Apollo cache	TBD

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