Include thread content in channel-level summaries /tldr and /tldr-since

[meetbryce]

Is your feature request related to a problem? Please describe.
I miss important information when summarizing channels with a good culture of using threads.

Describe the solution you'd like
When using the channel-level features, I want thread replies to be accounted for so I don't miss out on the important context of threaded conversations.

Describe alternatives you've considered
I can go back and generate thread summaries for each thread, but that's a hassle.

Additional context
Is simply generating and incorporating a thread summary the best experience when reading the summary or is something more sophisticated required?

How best is the parallel nature of the conversations accounted for?