ui5-button: Add Badge

[DMihaylova]

Background
A button serves the purpose of triggering an action. ​There are use cases where the user needs to collect a number of items on various pages before triggering an action. This is for example the typical basket use case on shopping sites. ​
In other use cases, the button serves in combination with a counter as a visual eyecatcher stating that the user’s attention is required for something.​
ui5-button needs to be enhanced to cater for such use cases.sap.m.Button already provides a badge with counter and attention badge.

Needed for compatibility reasons and also requested here: https://sap.stackenterprise.co/questions/60505

Need
As an application developer,
I'd like to be able to give signs to the users whenever an action from their side is needed
so they couldn't miss something important.

Acceptance criteria
ui5-button could display a badge (both counter and attention one).

[ui5-webcomponents-bot]

🎉 This issue has been resolved in version v2.7.0-rc.2 🎉

The release is available on v2.7.0-rc.2

Your semantic-release bot 📦🚀