Add reply hint to mail text (#22459)

Addition to #22056

This PR adds a hint to mail text if replies are supported.
I can't tell if the text structure is supported in every language. Maybe
we need to put the whole line in the translation file and use
parameters.

options/locale/locale_en-US.ini

@@ -365,6 +365,7 @@ password_pwned_err = Could not complete request to HaveIBeenPwned
 
 [mail]
 view_it_on = View it on %s
+reply = or reply to this email directly
 link_not_working_do_paste = Not working? Try copying and pasting it to your browser.
 hi_user_x = Hi <b>%s</b>,
 

services/mailer/mail.go

@@ -274,6 +274,7 @@ func composeIssueCommentMessages(ctx *mailCommentContext, lang string, recipient
 		"ActionName":      actName,
 		"ReviewComments":  reviewComments,
 		"Language":        locale.Language(),
+		"CanReply":        setting.IncomingEmail.Enabled && commentType != issues_model.CommentTypePullRequestPush,
 		// helper
 		"locale":    locale,
 		"Str2html":  templates.Str2html,

templates/mail/issue/default.tmpl

@@ -84,7 +84,7 @@
 	<p>
 		---
 		<br>
-		<a href="{{.Link}}">{{.locale.Tr "mail.view_it_on" AppName}}</a>.
+		<a href="{{.Link}}">{{.locale.Tr "mail.view_it_on" AppName}}</a>{{if .CanReply}} {{.locale.Tr "mail.reply"}}{{end}}.
 	</p>
 	</div>
 </body>