…hanges (elastic#190019)

## Summary
Issue: elastic#190018

Implement rule specific flapping support for create and update Rule API.
The new property on the rule is named `flapping`;

```
flapping: {
  look_back_window: number;
  status_change_threshold: number;
}
```

Also make changes in the task runner to use the rule's flapping settings
if it exists. Otherwise use the global flapping setting.

# To test
1. Go to
`x-pack/plugins/triggers_actions_ui/public/common/constants/index.ts`
and turn `IS_RULE_SPECIFIC_FLAPPING_ENABLED` to `true`
2. Create a rule with a rule specific flapping setting, generate the
alert and let it flap
3. Assert that the flapping is now using the rule specific flapping
4. Turn space flapping off
5. Assert that it no longer flaps despite having a rule specific
flapping
6. Try deleting/adding back the rule specific flapping via the UI and
verify everything works.

### Checklist
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

---------

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>
(cherry picked from commit edd61f6)