Feature/Idea - Bank holidays in alert node

Hi Team,

That could be very useful to be able to define list of day for bank holidays for attach them to a dedicated rules.

**Reason**
During bank holidays, activity (e-commerce/platform/network) are not the same as weekend or week days. For avoid a flood of alert during those days (bank holidays),

**How**
Maybe a filter or something like that will be very interesting in alert node.
Only the days & the month should be defined because that's recurrent every year. Format should be defined and documented : MM/DD or DD/MM or MM-DD or DD-MM
Something inside alert node as :
```
|alert
.bankholidays('01/05','02/03',)
.critbankholidays(lambda:)
```

Again here this proposal is an idea and i'm sure you'll provide us a better way for manage this.

No implementation file or test is named. Start by locating the alert node and its rule or filter handling, then review how recurring calendar conditions are represented and documented. Done means agreeing on the holiday-date format and behavior before implementing and testing the feature.

Written by the indexing model from the issue text.