Use config to select CodecPipeline and Codec implementations

[normanrz]

We want users to be able to choose their own codec pipeline and codec implementations. We need to use the config system to make that configurable. For that, the codec registry needs to deal with multiple codec implementations for the same name.

[normanrz]

The same should probably be used for (ND)Buffer implementations (see #1826). cc @madsbk