ingest: thread Slack notifications

[joverlee521]

Context

We get multiple Slack notifications per ingest run, so it would be cleaner to have these notifications threaded.

Possible Solution

• See ncov workflow for example of how this can be done with PersistentDict.

• Maybe another way we can go about this is edit the global Snakemake config to store the thread_ts? (Just a thought, haven't really tested if this is possible...)

[jameshadfield]

Maybe another way we can go about this is edit the global Snakemake config to store the thread_ts

This dosn't work (unfortunately) because each rule gets a copy of the config, which prevents this message-passing approach. PersistentDict was the only solution I could get to work (short of writing to a small file), but it's tricky to debug as when running locally a new snakemake run will still have access to the previous dict which can get confusing (it works for automated runs as they're in a new worker / environment).