Immutable configuration

[mversic]

I would prefer config to have private fields with constructors and getters for the following reasons:

1. consistency - access to some fields has to be done through getters because the value has to be converted
2. maintaining invariants - sometimes config params are interdependent,
   3. future proofing - we can change the underlying type without affecting the API

setters we can but don't even have to have. I wouldn't mind if the config structs were completely immutable. If we do decide to have setters we can put validation logic into them. But I would prefer to not have setters at least atm

[mversic]

you can find more info in discussion here

[0x009922]

@VAmuzing, you might need to consider changes https://github.com/hyperledger/iroha/pull/4456

[0x009922]

@mversic is it still relevant?

[mversic]

yes