This prep commit replaces the 'wildcard' keyword in the codebase
with 'stream_wildcard' at some places for better readability, as
we plan to introduce 'topic_wildcards' as a part of the
'@topic mention' project.
Currently, 'wildcards = ["all", "everyone", "stream"]' which is an
alias to mention everyone in the stream, hence better renamed as
'stream_wildcards'.
Eventually, we will have:
'stream_wildcard' as an alias to mention everyone in the stream.
'topic_wildcard' as an alias to mention everyone in the topic.
'wildcard' refers to 'stream_wildcard' and 'topic_wildcard' as a whole.
Prakhar Pratyush