Add Retry Policy in Eventbridge rule targets

[deechauhan]

This is a Feature Proposal

Description

• I have a step function configuration which is triggered by a Eventbridge rule. I want to use a custom RetryPolicy rather than the default 24 hours one. See AWS docs here.
• Currently RetryPolicy is not added in targets as part of AWS::Events::Rule. Related documentation on this can be found here.

Note: I'm willing to submit a PR for this