Upload crashes to collab directly (#8649)

This lets us run rustc_demangle on the backtrace, which helps the Slack
view significantly.

We're also now uploading files to digital ocean's S3 equivalent (with a
1 month expiry) instead of to Slack.

This PR paves the way for (but does not yet implement) sending this data
to clickhouse too.

Release Notes:

- N/A