MM-21552: Adding SaveMultiple to posts (#13766)

* Adding SaveMultiple to posts

* Improving tests

* fixing i18n

* Fixing tests

* Improving testing on top of Save and SaveMultiple

* Fixing shadow variables

* Addressing some PR comments

* More clear update post test

* Addressing some PR comments

* Addressing some PR comments and simplifying the code

* Improting replies in bulk too

* Fixing reply count and processing last imported replies

* Adding OverwriteMultiple to posts aggregating everything in the same transaction

* Adding 2 pending tests to implement

* Adding tests for overwrite multiple posts

* Adding tests for TeamStore.GetByNames method

* Fixing shadow variables

* Addressing PR comments

* Extracting i18n strings

* Fixing tests

* Fixing tests

* Adding more test cases

* Using a variable instead of a fake timestamp

cmd/mattermost/commands/sampledata.go

@@ -325,6 +325,11 @@ func sampleDataCmdF(command *cobra.Command, args []string) error {
 		user2 := allUsers[rand.Intn(len(allUsers))]
 		channelLine := createDirectChannel([]string{user1, user2})
 		encoder.Encode(channelLine)
+	}
+
+	for i := 0; i < directChannels; i++ {
+		user1 := allUsers[rand.Intn(len(allUsers))]
+		user2 := allUsers[rand.Intn(len(allUsers))]
 
 		dates := sortedRandomDates(postsPerDirectChannel)
 		for j := 0; j < postsPerDirectChannel; j++ {
@@ -344,6 +349,17 @@ func sampleDataCmdF(command *cobra.Command, args []string) error {
 		}
 		channelLine := createDirectChannel(users)
 		encoder.Encode(channelLine)
+	}
+
+	for i := 0; i < groupChannels; i++ {
+		users := []string{}
+		totalUsers := 3 + rand.Intn(3)
+		for len(users) < totalUsers {
+			user := allUsers[rand.Intn(len(allUsers))]
+			if !sliceIncludes(users, user) {
+				users = append(users, user)
+			}
+		}
 
 		dates := sortedRandomDates(postsPerGroupChannel)
 		for j := 0; j < postsPerGroupChannel; j++ {