Add country flag tooltips in wiki

[Swekka]

Closes #10661

[notbakaneko]

I'm pretty sure we don't want to be doing a db query for every single flag

[Swekka]

I just realized that if AU happens to be in the test db this test will always fail, since the actual html will have a title but the expected won't, but I have no idea what to do about that since the countries in the test db are always random

[notbakaneko]

I don't think we want to make a network request to redis for every flag either; use a local cache like https://github.com/ppy/osu-web/blob/3b91b06/app/Libraries/Groups.php or https://github.com/ppy/osu-web/blob/3b91b06/app/Libraries/Medals.php does it.

[notbakaneko]

I mean making a service object to cache the country names like Groups does and adding it to AppServiceProvider https://github.com/ppy/osu-web/blob/master/app/Providers/AppServiceProvider.php#L39-L43

[notbakaneko]

Fetch the countries (preferably just the name and country code) once, store it in an a Map or keyed array and do the lookup against the Map/array as needed.

[notbakaneko]

    private function allByCode(): Collection
    {
        return $this->memoize(__FUNCTION__, fn () => Country::get(['acronym', 'name'])->keyBy('acronym'));
    }

    public function byCode(string $code): ?Country
    {
        return $this->allByCode()->get($code);
    }

[notbakaneko]

this is needed for LocalCacheManager to manage resetting the local cache with resetMemoized()