fix(integration): Fix timeout error when adding slack integration rules if org has many channels (SEN-231)
fix(integration): Fix timeout error when adding slack integration rules if org has many channels (SEN-231)

https://slack.com/api/channels.list is just timing out for orgs with a lot of channels. This
endpoint is actually deprecated, but changing to the conversations api is a little more work so
punting on it for the moment. Through testing I found that just adding a limit (even if the limit is
higher than the number of returned channels) causes the endpoint to return quickly again, so I guess
it triggers some optimization.

Also started filtering out archived channels, since there's no reason to try and set up an alert for
a channel that is archived.

beeftornado/sentry,mvaled/sentry,mvaled/sentry,mvaled/sentry,beeftornado/sentry,mvaled/sentry,mvaled/sentry,beeftornado/sentry,mvaled/sentry