When a Slack-integrated channel is archived, posting from Chatwoot
raises `Slack::Web::Api::Errors::IsArchived` in `SendOnSlackJob`, which
retries and can end up in dead jobs. This can be reproduced by archiving
the connected Slack channel for a valid hook and creating outgoing
messages. This change adds `IsArchived` to the existing handled Slack
API rescue path in
`Integrations::Slack::SendOnSlackService#send_message`, so
archived-channel failures now follow the same flow as related Slack
failures (`prompt_reauthorization!` + `disable`) instead of bubbling and
retrying repeatedly. I tested this by running `bundle exec rubocop
lib/integrations/slack/send_on_slack_service.rb` (with `rbenv`
initialized), and it passes with no offenses.
Sentry issue: https://chatwoot-p3.sentry.io/issues/7150427066/
c7193c7917