Rename the existing 'wildcard_mentioned' flag to
'stream_wildcard_mentioned'.
The 'wildcard_mentioned' flag is deprecated and exists for
backwards compatibility.
We have two separate flags for stream and topic wildcard mentions,
i.e., 'stream_wildcard_mentioned' and 'topic_wildcard_mentioned',
respectively.
* stream wildcard mentions: `@all`, `@everyone`, and `@stream`
* topic wildcard mentions: `@topic`
The `wildcard_mentioned` flag is included in the events and
API response if either `stream_wildcard_mentioned` or
`topic_wildcard_mentioned` is set.
This commit renames the two unused and historical bits of the
'fields' bitfield of the 'UserMessage' and 'ArchivedUserMessage'
tables.
* 'summarize_in_home' to 'topic_wildcard_mentioned'
* 'summarize_in_stream' to 'group_mentioned'
The 'group_mentioned' flag doesn't affect the feature,
but completing the work here helps to save future migration
and indexing efforts on the UserMessage table, as we plan to
use this flag in the future for group mentions.
The unused bits may have old data; we'll clear that in
a separate commit.
It creates the 'zerver_usermessage_any_mentioned_message_id'
index concurrently.
