account-wizard: automatically replace imap.* with smtp.*

Many email providers use the imap sub-domain for imap and the smtp
sub-domain for smtp. FastMail is an example of this[1]. This is a small
quality-of-life improvement which automatically replaces imap.* with
smtp.* when going from the imap screen to the smtp screen in the wizard

[1]: https://www.fastmail.com/help/technical/servernamesandports.html

widgets/account-wizard.go

@@ -105,7 +105,12 @@ func NewAccountWizard(conf *config.AercConfig, aerc *Aerc) *AccountWizard {
 		wizard.smtpUri()
 	})
 	wizard.imapServer.OnChange(func(_ *ui.TextInput) {
-		wizard.smtpServer.Set(wizard.imapServer.String())
+		imapServerURI := wizard.imapServer.String()
+		smtpServerURI := imapServerURI
+		if strings.HasPrefix(imapServerURI, "imap.") {
+			smtpServerURI = strings.Replace(imapServerURI, "imap.", "smtp.", 1)
+		}
+		wizard.smtpServer.Set(smtpServerURI)
 		wizard.imapUri()
 		wizard.smtpUri()
 	})