Change `join_on` translation to `joined_on` and include placeholder for the date (#24550)

The correct thing to do is to translate the entire phrase into a single
string. The previous translation assumed all languages have a space
between the "joined on" and the date (and that "joined on" comes before
the date).

Some languages, like Hebrew, have no space between the "joined on" and
the date. For example:
```ini
joined_on=נרשם ב-%s
```
("joined" becomes נרשם, "on" is ב and when paired with a date we use a
dash to connect ב with the date)

options/locale/locale_en-US.ini

@@ -559,7 +559,7 @@ target_branch_not_exist = Target branch does not exist.
 
 [user]
 change_avatar = Change your avatar…
-join_on = Joined on
+joined_on = Joined on %s
 repositories = Repositories
 activity = Public Activity
 followers = Followers

templates/explore/organizations.tmpl

@@ -23,7 +23,7 @@
 								{{svg "octicon-link"}}
 								<a href="{{.Website}}" rel="nofollow">{{.Website}}</a>
 							{{end}}
-							{{svg "octicon-clock"}} {{$.locale.Tr "user.join_on"}} {{DateTime "short" .CreatedUnix}}
+							{{svg "octicon-clock"}} {{$.locale.Tr "user.joined_on" (DateTime "short" .CreatedUnix) | Safe}}
 						</div>
 					</div>
 				</div>

templates/explore/users.tmpl

@@ -18,7 +18,7 @@
 								{{svg "octicon-mail"}}
 								<a href="mailto:{{.Email}}" rel="nofollow">{{.Email}}</a>
 							{{end}}
-							{{svg "octicon-clock"}} {{$.locale.Tr "user.join_on"}} {{DateTime "short" .CreatedUnix}}
+							{{svg "octicon-clock"}} {{$.locale.Tr "user.joined_on" (DateTime "short" .CreatedUnix) | Safe}}
 						</div>
 					</div>
 				</div>

templates/repo/user_cards.tmpl

@@ -18,7 +18,7 @@
 					{{else if .Location}}
 						{{svg "octicon-location"}} {{.Location}}
 					{{else}}
-						{{svg "octicon-clock"}} {{$.locale.Tr "user.join_on"}} {{DateTime "short" .CreatedUnix}}
+						{{svg "octicon-clock"}} {{$.locale.Tr "user.joined_on" (DateTime "short" .CreatedUnix) | Safe}}
 					{{end}}
 				</div>
 			</li>

templates/user/profile.tmpl

@@ -73,7 +73,7 @@
 									</li>
 								{{end}}
 							{{end}}
-							<li>{{svg "octicon-clock"}} {{.locale.Tr "user.join_on"}} {{DateTime "short" .ContextUser.CreatedUnix}}</li>
+							<li>{{svg "octicon-clock"}} {{.locale.Tr "user.joined_on" (DateTime "short" .ContextUser.CreatedUnix) | Safe}}</li>
 							{{if and .Orgs .HasOrgsVisible}}
 							<li>
 								<ul class="user-orgs">