fix(AlarmFactory): Fix wording for actionsSuppressorExtensionPeriod prop to use 'duration' instead of 'time in seconds' (#519)

### Description
No code logic changes.

Unfortunately missed changing `actionsSuppressorExtensionPeriod` prop
description to use "duration" instead of "time in seconds". The "time in
seconds" descriptor is used in [CloudFormation
documentation](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-cloudwatch-compositealarm.html),
but since the prop type required by CDK `CompositeAlarm` is `Duration`,
it's more accurate to use "duration" (and to be consistent with the [CDK
Composite Alarm
definition](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_cloudwatch.CompositeAlarm.html)).

Note: This wording change was already done for
`actionsSuppressorWaitPeriod`; only `actionsSuppressorExtensionPeriod`
was missed.

### Testing
- `yarn build` -- no code logic changes so no additional unit tests
necessary.

---

_By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license_

Co-authored-by: Jonathan Luo <[email protected]>

Author: jonathan-luo

API.md

@@ -398,7 +398,7 @@ export interface AddCompositeAlarmProps {
   readonly actionsSuppressor?: IAlarm;
 
   /**
-   * The maximum time in seconds that the composite alarm waits after suppressor alarm goes out of the ALARM state.
+   * The maximum duration that the composite alarm waits after suppressor alarm goes out of the ALARM state.
    * After this time, the composite alarm performs its actions.
    *
    * @default - 60 seconds