#933: fix: Fixes output of LPUSH command

[Aditya-Chowdhary]

Fixes #933 by returning the length instead of OK.

Minor side change - Integration test for RPUSH used LPUSH command like below, which was fixed https://github.com/DiceDB/dice/blob/887d693113e266c8525c75b103346ced5fbdf997/integration_tests/commands/async/deque_test.go#L124

Would also like to point out the existence of a duplicate issue #961