*SendViaMarketingCloud* - _(SendEmailViaMC)_ - Allow a messageKey to be specified as input in the action

[lemerv]

The messageKey attribute is very useful for transactional sends. Details are here: https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/sendMessageSingleRecipient.html

Is your feature request related to a problem? Please describe. Yes, documented here: https://github.com/alexed1/LightningFlowComponents/issues/1236

Describe the solution you'd like What would be a great improvement to the SendEmailViaMC action is to have another input field for specifying a messageKey. This be what gets appended to the end of the callout url. For example:

Input value for messageKey = 1234

Final callout url to the transactional api = https://mcxxxxxxxxxxxxxxxxxxxxxxx.rest.marketingcloudapis.com/messaging/v1/email/messages/1234

Describe alternatives you've considered This action does already create a messageKey (looks to be a timestamp), but this is not available as an output from the action, so is not really useful.

Additional context Add any other context or screenshots about the feature request here.