[CLD-6894] Add 60, 30, and 7 day reminder emails for Cloud Renewals (#25883)

* Add email notifications for Cloud Renewals

* Updates

* Updates

* Update app-layers

* make build-templates

* Add ability to set an env variable as a unix timestamp in s as the current date when getting DaysToExpiration

* Add a mechanism to ensure at least one admin receives every email

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Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Gabe Jackson <3694686+gabrieljackson@users.noreply.github.com>

server/public/model/system.go

@@ -38,6 +38,7 @@ const (
 	SystemHostedPurchaseNeedsScreening     = "HostedPurchaseNeedsScreening"
 	AwsMeteringReportInterval              = 1
 	AwsMeteringDimensionUsageHrs           = "UsageHrs"
+	CloudRenewalEmail                      = "CloudRenewalEmail"
 )
 
 const (