This changes the hashtag search to first do a lookup to find
results where the slug exactly matches the
search term. Now when we search for hashtags, the
exact matches will be found first and put at the top of
the results.
`ChatChannelFetcher` has also been modified here to allow
for more options for performance -- we do not need to
query DM channels for secured IDs when looking up or searching
channels for hashtags, since they should never show in
results there (they have no slugs). Nor do we need to include
the channel archive records.
Also changes the limit of hashtag results to 20 by default
with a hidden site setting, and makes it so the scroll for the
results is overflowed.
274b21663e