Add no-cookie variants of the Google Analytics templates

The current full set of options for GA is now:

```toml
[privacy]
[privacy.googleAnalytics]
disable = false
respectDoNotTrack = true
anonymizeIP = true
useSessionStorage = true
```

Fixes #4775

config/privacy/privacyConfig.go

@@ -45,6 +45,9 @@ type Disqus struct {
 type GoogleAnalytics struct {
 	Service `mapstructure:",squash"`
 
+	// Enabling this will disable the use of Cookies and use Session Storage to Store the GA Client ID.
+	UseSessionStorage bool
+
 	// Enabling this will make the GA templates respect the
 	// "Do Not Track" HTTP header. See  https://www.paulfurley.com/google-analytics-dnt/.
 	RespectDoNotTrack bool

config/privacy/privacyConfig_test.go

@@ -35,6 +35,7 @@ disable = true
 disable = true
 respectDoNotTrack = true
 anonymizeIP = true
+useSessionStorage = true
 [privacy.instagram]
 disable = true
 simple = true
@@ -61,6 +62,7 @@ simple = true
 	assert.True(pc.GoogleAnalytics.Disable)
 	assert.True(pc.GoogleAnalytics.RespectDoNotTrack)
 	assert.True(pc.GoogleAnalytics.AnonymizeIP)
+	assert.True(pc.GoogleAnalytics.UseSessionStorage)
 	assert.True(pc.Instagram.Disable)
 	assert.True(pc.Instagram.Simple)
 	assert.True(pc.SpeakerDeck.Disable)