Add support for settings injection

### Problem
As currently pointed out in #2600, v5 of NServiceBus no longer has a hook to assign config settings to `IHandleMessages<T>` types.

This PR intention is to brainstorm the available options to expose back this feature.

### Current workaround
- User can create a wrapper class that exposes the settings  
Not the nicest solution, specially if there is only 1 setting
- User registers the `IHandleMessages<T>` class themselves  
This option has the issue of putting the burden of know the dependency lifecycle on the user
- User reads the settings from the `IHandleMessages<T>` class themselves  
Violates the SRP
- User configures this in his own container of choice and then registers it with NServiceBus

### Current limitations in previous versions
Only property injection is supported, no ctor injection :disappointed: 

### Future
With v6 taking shape, how do we see such a feature exposed ?
Do we take the stance that user configures this in his own container of choice and then registers it with NServiceBus ?

### Proposal
Not that I like this but, I can't see a different workaround.
```c#
config.InitializeHandlerProperty<MyHandler>(h => h.MyProp, myvalue);
```