MM-16369: include potential subpath in emails (#11311)

* MM-16369: include potential subpath in emails

Various email templates were extracting the `Host` but not the `Path` from the SiteURL, excluding a potential subpath defined therein.

* improve coverage of condenseSiteURL

app/email_test.go

@@ -0,0 +1,28 @@
+package app
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestCondenseSiteURL(t *testing.T) {
+	require.Equal(t, "", condenseSiteURL(""))
+	require.Equal(t, "mattermost.com", condenseSiteURL("mattermost.com"))
+	require.Equal(t, "mattermost.com", condenseSiteURL("mattermost.com/"))
+	require.Equal(t, "chat.mattermost.com", condenseSiteURL("chat.mattermost.com"))
+	require.Equal(t, "chat.mattermost.com", condenseSiteURL("chat.mattermost.com/"))
+	require.Equal(t, "mattermost.com/subpath", condenseSiteURL("mattermost.com/subpath"))
+	require.Equal(t, "mattermost.com/subpath", condenseSiteURL("mattermost.com/subpath/"))
+	require.Equal(t, "chat.mattermost.com/subpath", condenseSiteURL("chat.mattermost.com/subpath"))
+	require.Equal(t, "chat.mattermost.com/subpath", condenseSiteURL("chat.mattermost.com/subpath/"))
+
+	require.Equal(t, "mattermost.com:8080", condenseSiteURL("http://mattermost.com:8080"))
+	require.Equal(t, "mattermost.com:8080", condenseSiteURL("http://mattermost.com:8080/"))
+	require.Equal(t, "chat.mattermost.com:8080", condenseSiteURL("http://chat.mattermost.com:8080"))
+	require.Equal(t, "chat.mattermost.com:8080", condenseSiteURL("http://chat.mattermost.com:8080/"))
+	require.Equal(t, "mattermost.com:8080/subpath", condenseSiteURL("http://mattermost.com:8080/subpath"))
+	require.Equal(t, "mattermost.com:8080/subpath", condenseSiteURL("http://mattermost.com:8080/subpath/"))
+	require.Equal(t, "chat.mattermost.com:8080/subpath", condenseSiteURL("http://chat.mattermost.com:8080/subpath"))
+	require.Equal(t, "chat.mattermost.com:8080/subpath", condenseSiteURL("http://chat.mattermost.com:8080/subpath/"))
+}