consider using OptionQuery instead of ValueQuery for more pallet storages

[brenzi]

ValueQuery just returns default if the storage is empty. That only makes sense in very few situations
It seems our migration to frameV2 defaulted to ValueQuery.

In the case of CommunityMetadata and possibly others I may question this choice.

@clangenb do you remember if there was a specific reason to use ValueQuery?

[clangenb]

No, the only reason I see is that it introduced less breaking changes in pallet code, as this was the default before. I do question some value queries too.