Networks and Sites: Use metadata api in `*_network_options functions.

Replace logic found in `get_network_option`, `update_network_option` and `delete_network_option` to use the metadata api. Using the metadata api has a number of benefits, such as consistency, default values and useful filters. This change also improves performance by priming the caches of all network options in a single database request. 

Props spacedmonkey, swissspidy, sc0ttkclark, johnjamesjacoby, flixos90, jeremyfelt, pento, peterwilsoncc, mukesh27, desrosj.
Fixes #37181

git-svn-id: https://develop.svn.wordpress.org/trunk@54080 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/load.php

@@ -743,6 +743,7 @@ function wp_start_object_cache() {
 				'site-details',
 				'site-options',
 				'site-transient',
+				'site_meta',
 				'rss',
 				'users',
 				'useremail',