sqldb: add global lock config options for postgres

Add two configuration options to control global lock usage for
different postgres database backends:

- ChannelDBWithGlobalLock: for channeldb access (default: false)
- WalletDBWithGlobalLock: for wallet database access (default: true)

These allow fine-grained control over which databases use global
locks, rather than hardcoding the behavior. This is a temporary
measure until the revocation log and wallet are migrated to native
SQL and become fully concurrent-safe.

sqldb/config.go

@@ -48,6 +48,8 @@ type PostgresConfig struct {
 	Timeout                 time.Duration `long:"timeout" description:"Database connection timeout. Set to zero to disable."`
 	MaxConnections          int           `long:"maxconnections" description:"The maximum number of open connections to the database. Set to zero for unlimited."`
 	SkipMigrations          bool          `long:"skipmigrations" description:"Skip applying migrations on startup."`
+	ChannelDBWithGlobalLock bool          `long:"channeldb-with-global-lock" description:"Use a global lock for channeldb access. This ensures only a single writer at a time but reduces concurrency. This is a temporary workaround until the revocation log is migrated to a native sql schema."`
+	WalletDBWithGlobalLock  bool          `long:"walletdb-with-global-lock" description:"Use a global lock for wallet database access. This ensures only a single writer at a time but reduces concurrency. This is a temporary workaround until the wallet subsystem is upgraded to a native sql schema."`
 	QueryConfig             `group:"query" namespace:"query"`
 }