Update to match rdkafka version 6.0.4

[bdurkovic]

• Added methods added in rdkafka 6.0.4
• Kept compatibility with php 7.x to match composer requirement in rdkafka 6.x
• Added parameters and return types where possible
• Added callback parameters in phpdoc

[bdurkovic]

@kwn no pressure, but any chance you could take a look at this? Is there anything else I could do to make this happen?

[kwn]

Hi @bdurkovic
Thank you for your contribution. At the moment I have almost no spare time due to some personal matters, but please give me a bit more time, and I'll look into the PR in the upcoming weeks. Thank you for your patience.