Introduce IoC / simple DI to improve extendibility

[RassK]

Why

Introduce very simple DI to make current solution more extendable.

What

Due full IoC containers add unnecessary complexity and reduce performance I would offer "Factory configurator" pattern.
Instead of hosting anything like IoC containers, factory configurator will take reference only for implementations of the concrete interfaces (see example below). OTel repo will host DefaultFactoryConfiguration and a distro will host eg: SplunkFactoryConfiguration where it could override the sub services / factories or construct whole implementation from scratch. Factory configuration type could be loaded either from environment variable, from static, etc. IFactoryConfiguration reference must be passed down the line (I expect it will be in the Tracer instance?)

This feature is connected to: #117

class SomeFactoryConfiguration : IFactoryConfiguration
{
   // Singleton services
   public IMyService { get; } = new MyDistroService();

   // Transient services
   public IMyFactory { get; } = new MyDistroFactory();
}

[pellared]

It is also related to #116

nit: I would prefer to have methods in interfaces than properties like

class SomeFactoryConfiguration : IFactoryConfiguration
{
   // Singleton services
   public IMyService MyService() => new MyDistroService();

   // Transient services
   public IMyFactory MyFactory() => new MyDistroFactory();
}

[RassK]

Leaving a note: We have to get rid of enums and prob return to constant string values. Enums are not extendable.

[macrogreg]

Closing since this is basically the same as #117