Adding send_at for Sendgrid

spec/support/custom_template_email.cr

@@ -7,7 +7,7 @@ class CustomTemplateEmail < Carbon::Email
     @headers = {} of String => String,
     @subject = "subject",
     @text_body : String? = nil,
-    @html_body : String? = nil
+    @html_body : String? = nil,
   )
   end
 

spec/support/fake_email.cr

@@ -9,7 +9,7 @@ class FakeEmail < Carbon::Email
     @headers = {} of String => String,
     @subject = "subject",
     @text_body : String? = nil,
-    @html_body : String? = nil
+    @html_body : String? = nil,
   )
   end
 

spec/support/fake_email_with_attachments.cr

@@ -9,7 +9,7 @@ class FakeEmailWithAttachments < Carbon::Email
     @headers = {} of String => String,
     @subject = "subject",
     @text_body : String? = nil,
-    @html_body : String? = nil
+    @html_body : String? = nil,
   )
   end
 

src/carbon_sendgrid_adapter.cr

@@ -46,6 +46,7 @@ class Carbon::SendGridAdapter < Carbon::Adapter
         "asm"              => {"group_id" => 0, "groups_to_display" => [] of Int32},
         "mail_settings"    => {sandbox_mode: {enable: sandbox?}},
         "attachments"      => attachments,
+        "send_at"          => email.send_at,
       }.compact
 
       # If Sendgrid sees an empty attachments array, it'll return an error

src/carbon_sendgrid_extensions.cr

@@ -24,6 +24,13 @@ module Carbon::SendGridExtensions
   def asm
     nil
   end
+
+  # Tell Sendgrid to send the email at this time.
+  # Value should be a unix timestamp integer
+  # https://www.twilio.com/docs/sendgrid/for-developers/sending-email/personalizations
+  def send_at
+    nil
+  end
 end
 
 class Carbon::Email