Integrated Alerting: Ability to delete alert rules

User Story: 

• As a PMM admin user, I need to be able to delete Alert Rule so it will be not executed and not presented in the system 

UI:

 Acceptance Criteria: 

• The user is able to click the Delete button. 
• The User is able to see the modal confirmation window before deleting the Alert Rule 
• As a User, when I trigger an action that successfully resolves, I can see a success notification.
• As a User, when I trigger an action that errors out, I can see an error notification.
• HTML title
• after the Delete button is pressed, the overlay is activated

Implementation details:

• code and PRs get pushed to percona-platform/grafana repository
• test coverage
• honor light/dark mode