structure Hello exposes public fields

[milyin]

Describe the release item

It was decided to not expose struct with public fields in zenoh API, using accessors instead.
This should be done for Hello structure: https://github.com/eclipse-zenoh/zenoh/blob/c-coverage/commons/zenoh-protocol/src/scouting/hello.rs#L105
The field versionfor example is internal and should not be exposed