PLT-7212: fix missing webhook post attachments (#7011)

* fix missing webhook post attachments

* make ProcessSlackAttachments return a new slice instead of modifying it

model/slack_attachment.go

@@ -33,8 +33,6 @@ type SlackAttachmentField struct {
 	Short bool        `json:"short"`
 }
 
-type SlackAttachments []*SlackAttachment
-
 // To mention @channel via a webhook in Slack, the message should contain
 // <!channel>, as explained at the bottom of this article:
 // https://get.slack.help/hc/en-us/articles/202009646-Making-announcements
@@ -51,9 +49,9 @@ func ExpandAnnouncement(text string) string {
 // can be found in the text attribute, or in the pretext, text, title and value
 // attributes of the attachment structure. The Slack attachment structure is
 // documented here: https://api.slack.com/docs/attachments
-func (a *SlackAttachments) Process() {
+func ProcessSlackAttachments(a []*SlackAttachment) []*SlackAttachment {
 	var nonNilAttachments []*SlackAttachment
-	for _, attachment := range *a {
+	for _, attachment := range a {
 		if attachment == nil {
 			continue
 		}
@@ -77,5 +75,5 @@ func (a *SlackAttachments) Process() {
 		}
 		attachment.Fields = nonNilFields
 	}
-	*a = nonNilAttachments
+	return nonNilAttachments
 }