Prepare monitoring

[themarolt]

We already have monitoring for Nango cloud connections but it uses message forwarding through Datadog and it's unreliable. We need to have our own way of posting slack messages - Joan can create a slack webhook that is used to post notifications to #cm-alerts channel. Perhaps we can also create one for staging env like #cm-staging-alerts or something similar.

Besides this the current monitoring for gerrit assumes 1 integrations row = 1 nango connection which won't be the case here so a different handling needs to be implemented for github here.