Builder API for configuring enclosed objects

[milyin]

Describe the feature

Summarizing discussion here: #656
We need to decide how to process optional internal structures in builder pattern. If structure is not optional, like Samplein PutBuilder, we can expose sample's encoding method from PutBuilder itself. But if the Sample is optional, like in GetBuilder, the setting of encoding should also add this sample.
Possible solutions:

• GetBuilder::encoding implicitly adds Sample
• GetBuilder provides some sub-builder, which explicilty adds default Sample and allows to set encoding
• Do not expose methods for configuring optional interlal structures
• something else?

[milyin]

Discussed with @Mallets
methods with_payload and with_encoding should be used for get operation
Consider removing Value type and flatten encoding and payload everywhere.

[milyin]

It was decided to make builders API as flat as possible. Value is already deconstructed to payload and encoding, QoS is accessed through priority, express etc.