Use global lock instead of NewExclusivePool to allow distributed lock between multiple Gitea instances (#31813)

Replace #26486 
Fix #19620

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Co-authored-by: Jason Song <i@wolfogre.com>

custom/conf/app.example.ini

@@ -2713,3 +2713,9 @@ LEVEL = Info
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; storage type
 ;STORAGE_TYPE = local
+
+;[global_lock]
+;; Lock service type, could be memory or redis
+;SERVICE_TYPE = memory
+;; Ignored for the "memory" type. For "redis" use something like `redis://127.0.0.1:6379/0`
+;SERVICE_CONN_STR =