Add aliases for `spo web alert` commands

[milanholemans]

The goal is to add aliases for the following commands:

Current command	Alias
spo web alert list	spo web rule list
spo web alert remove	spo web rule remove

Since SharePoint alerts are deprecated, I suggest that we rename the entire command to spo web rule and add the current spo web alert name as alias. This makes sure that we can easily remove the alias in the next major version when SP alerts are EoL.

[waldekmastykarz]

I think rule is less obvious as to what it does, comparing to alert. That said, if alerts are EoL then the decision has been made and it'll be a matter of time until folks get used to the new name. Perhaps it's something that we should consider clarifying in our docs in case someone keeps looking for alert-related functionality.