Add timeout env to Lab chart

There is a KEEP_ALIVE_TIMEOUT_MS ENV var which defaults to 65 seconds, meaning the Lab will hold connection for 65 seconds. I would be good to add this ENV var to example in README like we did with QUICK CONNECT envs. 

How it looks for 300sec:
`KEEP_ALIVE_TIMEOUT_MS=300000`

Related: https://memgraph.slack.com/archives/C01BRQLQVAA/p1718787983847609?thread_ts=1718695126.104139&cid=C01BRQLQVAA