{scopes,collections}-details stats can't be accessed (enoent)

This patch simplified keeping a consistent list of stat groups, adding StatsGroupManager and an enum value for each valid group.

However, ep-engine initially filters some groups by prefix:

    if (cb_isPrefix(key, "collections")) {

        return doCollectionStats(

                c, add_stat, std::string(key.data(), key.size()));

    }

and later checks the rest of the key:

if (cb_isPrefix(statKey, "collections-details")) {

        return doCollectionDetailStats(bucket, collector, arg);

    }

It appears this was missed; collections and collections-byid are both listed in StatsGroupManager/StatGroupId and are still accessible whereas collections-details is not, and is thus rejected by StatsCommandContext with cb::engine_errc::no_such_key.

scopes-details appears similarly affected.

collections-details does appear to be requested for a cbcollect.

collections-details and scopes-details should be added to StatGroupId and StatsGroupManager entries.