Make key names case-insensitive in PHP

[prateek-kumar-improving]

Make sure the keys like refresh_topology_from_initial_nodes are case insensitive when passed by the user.

Currently, these keys are case sensitive. It won't get picked up if the casing doesn't match. For now, the constant makes it easier to do this safely but doesn't guarantee it.

For now these keys are required to be passed as lower case for the code to work:
• refresh_topology_from_initial_nodes
• connection_timeout
• use_insecure_tls
• host, port
• username, password
• type, key
Note: There might be more keys that are case sensitive. Search the code again.

Possible solution:

1. iterate over the keys in the hash and compare them case-insensitively against known keys.
2. Check if possible to make this work using some built-in Zend way.

Evaluate other solutions as well.