Autodisabling blocked subscriptions

[androndo]

Today some subscriptions may repeat failed sendings about 50+ times, because:

• telegram bot blocked
• slack channel archieved
• wrong contact address
• etc.

But some reasons is ok: timeouts or others (?), we need pass them.

This sending attempts generate unneccessary activity and trash collected at logs.

Possible way:
Add some euristic to check notification fail reasons and attempts count, and disable subscription automatically.
Add to admin page: enable/disable this feature and abillity to restore (enable all disabled) in case of fuckups.
Send banned count metric.