Update NEWS and UPGRADING wrt. opcache.cache_id [ci skip]

Author: cmb69

NEWS

@@ -16,6 +16,7 @@ PHP                                                                        NEWS
 
 - Opcache:
   . Fixed bug #78271 (Invalid result of if-else). (Nikita)
+  . Added new INI directive opcache.cache_id (Windows only). (cmb)
 
 - Recode:
   . Unbundled the recode extension. (cmb)

UPGRADING

@@ -610,6 +610,10 @@ PHP 7.4 UPGRADE NOTES
 - configure now regards additional CFLAGS and LDFLAGS set as environment
   variables.
 
+- OPcache now supports an arbitrary amount of separate caches per user via the
+  the INI directive opcache.cache_id. All processes with the same cache ID and
+  user share an OPcache instance.
+
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 13. Migration to pkg-config
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