Set batched notification email timestamps to user TZ (#26121)

* refactor: migrate getFormattedPostTime to utils

Move app.getFormattedPostTime to utils and export along with its struct

* Set batch notification post times to user TZ

* default useMilitaryTime to false in batched email

If there is an error reading the user's preference for useMilitaryTime,
default to false, as that should be the default value if the user never
sets it.

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/utils/time.go

@@ -4,7 +4,12 @@
 package utils
 
 import (
+	"fmt"
+	"strconv"
 	"time"
+
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/shared/i18n"
 )
 
 func MillisFromTime(t time.Time) int64 {
@@ -28,3 +33,45 @@ func EndOfDay(t time.Time) time.Time {
 func Yesterday() time.Time {
 	return time.Now().AddDate(0, 0, -1)
 }
+
+type FormattedPostTime struct {
+	Time     time.Time
+	Year     string
+	Month    string
+	Day      string
+	Hour     string
+	Minute   string
+	TimeZone string
+}
+
+func GetFormattedPostTime(user *model.User, post *model.Post, useMilitaryTime bool, translateFunc i18n.TranslateFunc) FormattedPostTime {
+	preferredTimezone := user.GetPreferredTimezone()
+	postTime := time.Unix(post.CreateAt/1000, 0)
+	zone, _ := postTime.Zone()
+
+	localTime := postTime
+	if preferredTimezone != "" {
+		loc, _ := time.LoadLocation(preferredTimezone)
+		if loc != nil {
+			localTime = postTime.In(loc)
+			zone, _ = localTime.Zone()
+		}
+	}
+
+	hour := localTime.Format("15")
+	period := ""
+	if !useMilitaryTime {
+		hour = localTime.Format("3")
+		period = " " + localTime.Format("PM")
+	}
+
+	return FormattedPostTime{
+		Time:     localTime,
+		Year:     strconv.Itoa(localTime.Year()),
+		Month:    translateFunc(localTime.Month().String()),
+		Day:      strconv.Itoa(localTime.Day()),
+		Hour:     hour,
+		Minute:   fmt.Sprintf("%02d"+period, localTime.Minute()),
+		TimeZone: zone,
+	}
+}