Add the ability to delete kudos posted by the Check-Ins Integration

[ocielliottc]

Is your feature request related to a problem? Please describe.
Currently, kudos are posted via the web-hook URL. Posting using that method does not allow for non-admins to delete those messages. To truly complete #2870, we need the ability to delete kudos posted to slack via the Check-Ins Integration.

Describe the solution you'd like
We need to move away from posting with the web-hook and post messages using the Slack API ChatPostMessageRequest. At that point, we should be able to delete messages using ChatDeleteRequest.

[ocielliottc]

Adds a delete method to SlackSender.
delete.patch