Add (configurable) delay to sending notifications

[hugalafutro]

Description

I have several machines utilising diun, but few of them run so many containers it kills the telegram notifications with following error (to clarify, i.e. from 40 containers 20 update, I get notification for 15 and then 5 errors (numbers illustrational)):

diun  | Sat, 04 Jan 2025 12:01:20 GMT ERR Telegram notification failed error="failed to execute POST request to sendMessage: Post \"https://api.telegram.org/bot[REDACTED]/sendMessage\": context deadline exceeded" image=ghcr.io/sdr-enthusiasts/docker-piaware:latest

I propose a setting to delay each subsequesnt notification after 1st by x seconds to combat this. I am aware this might be telegram specific, but I'd wager other notif services won't enjoy spammy requests either.

Thanks for your consideration.