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

crates/collab/src/lib.rs

@@ -127,6 +127,7 @@ pub struct Config {
     pub blob_store_bucket: Option<String>,
     pub zed_environment: Arc<str>,
     pub zed_client_checksum_seed: Option<String>,
+    pub slack_panics_webhook: Option<String>,
 }
 
 impl Config {