lncfg+scripts: use configurable global lock for postgres backends

Replace hardcoded WithGlobalLock assignment with configurable
options wallet postgres backends. Also add the WithGlobalLock
option to the channeldb table for postgres backends.

Defaults:
- channeldb: false (allow concurrent access)
- wallet: true (maintain safe single-writer behavior)

Users can now override these defaults via:
- db.postgres.channeldb-with-global-lock
- db.postgres.walletdb-with-global-lock

This gives operators flexibility while maintaining safe defaults
until full native SQL migration is complete.

Moreover exclude db.postgres.walletdb-with-global-lock check
in the sample config file script. We cannot easily check the
correct default because we set it later in the LND startup
sequence so we exclude it.

scripts/check-sample-lnd-conf.sh

@@ -59,7 +59,7 @@ OPTIONS_NO_LND_DEFAULT_VALUE_CHECK="channel-max-fee-exposure adminmacaroonpath \
     backupfilepath maxchansize bitcoin.chaindir bitcoin.defaultchanconfs \
     bitcoin.defaultremotedelay bitcoin.dnsseed signrpc.signermacaroonpath \
     walletrpc.walletkitmacaroonpath chainrpc.notifiermacaroonpath \
-    routerrpc.routermacaroonpath" 
+    routerrpc.routermacaroonpath db.postgres.walletdb-with-global-lock" 
 
 
 # EXITCODE is returned at the end after all checks are performed and set to 1