config+sqldb: make native SQL query config options configurable

Here, we make the sql query option params (batch size and pagination
size) configurable. The defaults for SQLite vs Postgres are still the
same but will be changed in an upcoming commit.

sample-lnd.conf

@@ -1601,6 +1601,12 @@
 ; Whether to skip executing schema migrations.
 ; db.postgres.skipmigrations=false
 
+; The maximum number of elements to use in a native-SQL batch query IN clause.
+; db.postgres.query.max-batch-size=5000
+
+; The maximum number of records to fetch at a time in a paginated query during
+; native-SQL calls.
+; db.postgres.query.max-page-size=10500
 
 [sqlite]
 
@@ -1617,6 +1623,13 @@
 ; The maximum amount of time to wait to execute a query if the db is locked.
 ; db.sqlite.busytimeout=5s
 
+; The maximum number of elements to use in a native-SQL batch query IN clause.
+; db.sqlite.query.max-batch-size=250
+
+; The maximum number of records to fetch at a time in a paginated query during
+; native-SQL calls.
+; db.sqlite.query.max-page-size=100
+
 ; Raw pragma option pairs to be used when opening the sqlite db. The flag
 ; can be specified multiple times to set multiple options.
 ; Default: