Add Locking API for quickly creating custom named locks.

[abose]

There should be a way to enter a named critical section with coco SQL client. Something similar to this API or an easier way to do this:

let lock = await db.lock("database.customLockName", leaseTimeoutMS);
// do my critical section things
await lock.extend(leaseTimeoutMS); // taking longer time than expected, increase lock lease time
// do my critical section things
await lock.release();

• leaseTimeoutMS should be application controlled as it depends on program correctness requirements and can be infinite.
• If deadlock arises, it will be an application task to recover.
• DB resources will not be spent to maintain locks. The locking compute will be fully maintained at the client lib.