feat: timeout configuration for client

[klopfdreh]

This PR is going allow the configuration of the timeout for prometheus-rsocket-proxy-clientto connect to the proxy-server and to push the data to the server.

Fixes: #86

[klopfdreh]

First I added the timeout as a static field which was not good, because if you use the builder a second time the newly created PrometheusRSocketClient would take the timeout of the previous one.

I then created another constructor to make it backwards compatible and added some convenient methods and also changed the timeout to a class member.

This way the timeout can be configured for each PrometheusRSocketClient differently.

[klopfdreh]

Update: I squashed the commits into one so that it can be easily merged.

[shakuzen]

Overall looks good. I left one review about the configuration property type. Some of the formatting changes will probably be undone if/when we apply the formatter plugin, but no need to worry too much about that since we don't have it configured currently.