Bug 1626997 - Toggle the network.preload pref on on all channels. r=dragana, a=jcristau

Afaict we've shipped this code via normandy or what not, so let's do
this.

Differential Revision: https://phabricator.services.mozilla.com/D101250

modules/libpref/init/StaticPrefList.yaml

@@ -8504,10 +8504,10 @@
   value: false
   mirror: always
 
-# Enables `<link rel="preload">` tag and `Link: rel=preload` respose header handling.
+# Enables `<link rel="preload">` tag and `Link: rel=preload` response header handling.
 - name: network.preload
   type: RelaxedAtomicBool
-  value: @IS_EARLY_BETA_OR_EARLIER@
+  value: true
   mirror: always
 
 # Whether to use the network process or not