Add methods for COV notification sending

[deimi]

Checklist

• [x] I've read and followed the Contribution Guide.
• [x] My commit messages reference affected issues and mention breaking changes if applicable.
• [x] I've updated / wrote inline documentation for the source code affected by my changes.
• [ ] All mandatory CI checks have passed (see when Pull Request has been submitted).

What does this Pull Request do

Adds client methods for sending confirmed and unconfirmed COV notifications.

I tried to make as less changes a possible to not brake any API or consistency. Therefore the methods have separate parameters for all notification data and not a single notification object. This way it keeps consistent with the subscribe method.
A separate refactoring, to have a single object parameter for all the notification data, of the subcribeCOV and COVNotification method should be done. Like in the eventNotification method.