[feature] Ability to set length limit for notifications

**Version and OS**
v0.40.1.1

**Is your feature request related to a problem? Please describe.**
If a homepage has multiple changes, the output of the notification can be quite long (with a lot of "changed"/"added"/"removed"). That is very long for the end-user.

**Describe the solution you'd like**
It would be nice if there is a limit for a notification length (global for all and watch specifiy) and a text which will be added if the output is longer.

**Describe the use-case and give concrete real-world examples**
```
There are a lot of changes on that watch. Please see the screenshot
```

**Additional context**
I know there is already a limit for telegram inside the code, but would be nice if that can be configured and the notification text can be replace with a text above.

Start by locating the notification-generation code and the existing Telegram length limit mentioned in the issue, then trace how watch-specific and global settings are handled. Done means configurable global and per-watch notification limits, with a configurable replacement text when output is truncated, while preserving the existing notification behavior.

Written by the indexing model from the issue text.