Show bot label next to username when rendering autor link if the user is a bot (#24943)

If the user is a bot, we'll add a label next to the author link that
says `bot`. I didn't localize `bot` because passing `locale` into the
`autorlink` template would require changing all calls.

# Example
`yardenshoham` is a bot.
## Before

![image](77390780-b763-4f0f-b358-bbccdbf17a5d)

## After

![image](72af342f-ee76-4337-95ad-4ecaba853fed)

---------

Signed-off-by: Yarden Shoham <git@yardenshoham.com>

models/user/user.go

@@ -406,6 +406,11 @@ func (u *User) IsIndividual() bool {
 	return u.Type == UserTypeIndividual
 }
 
+// IsBot returns whether or not the user is of type bot
+func (u *User) IsBot() bool {
+	return u.Type == UserTypeBot
+}
+
 // DisplayName returns full name if it's not empty,
 // returns username otherwise.
 func (u *User) DisplayName() string {