Optimize each page's query so the GraphQL result is cached

[janosrusiczki]

Spawned from #330

Ideally the SQL queries should be run once, but it needs to be investigated if it's worth implementing the whole caching mechanism.

I'm leaning towards NO because:

1. When a visitor will load a page the SQL queries will be doubled but on subsequent navigation only GraphQL will be accessed;
2. A search engine will only see the shadow page and GraphQL won't be accesed so SQL queries will only be run once - Apparently this is not true, at least Google understands the JS page;
3. The current version of Apollo for Vue 3 didn't seem to support caching (at least not as easily as the previous version). Eventually I figured this one out.