Revert "Drop MinervaEnableSiteNotice"

This reverts commit 33e5c1eb79.

I talked to Gergo (tgr) about this and he's convinced me
that probably I want to be more conservative 
and incremently roll the sitenotices
out first. With that in mind I'm going to revert this change
and do a config flag instead.

Bug: T254391
Change-Id: If0f214d23a012fb4ae3e1dff1728f746a22f142a

README.md

@@ -28,6 +28,14 @@ The following configuration options will apply only to the default mobile skin -
 Whether to show the language switcher button even if no languages are available
 for the page.
 
+#### $wgMinervaEnableSiteNotice
+
+* Type: `Boolean`
+* Default: `false`
+
+Controls whether site notices should be shown.
+See <https://www.mediawiki.org/wiki/Manual:$wgSiteNotice>.
+
 #### $wgMinervaCountErrors
 * Type: `Boolean`
 * Default: `false`

includes/Skins/SkinMinerva.php

@@ -589,9 +589,11 @@ class SkinMinerva extends SkinTemplate {
 	protected function prepareBanners( BaseTemplate $tpl ) {
 		// Make sure Zero banner are always on top
 		$banners = [ '<div id="siteNotice"></div>' ];
-		$siteNotice = $this->getSiteNotice();
-		if ( $siteNotice ) {
-			$banners[] = $siteNotice;
+		if ( $this->getConfig()->get( 'MinervaEnableSiteNotice' ) ) {
+			$siteNotice = $this->getSiteNotice();
+			if ( $siteNotice ) {
+				$banners[] = $siteNotice;
+			}
 		}
 		$tpl->set( 'banners', $banners );
 		// These banners unlike 'banners' show inside the main content chrome underneath the

skin.json

@@ -33,6 +33,9 @@
 				0
 			]
 		},
+		"MinervaEnableSiteNotice": {
+			"value": false
+		},
 		"MinervaApplyKnownTemplateHacks": {
 			"value": false
 		},