WIP - Proof of concept how to include openmetric exemplars.

[hrodic]

No description provided.

[hrodic]

This is just and idea on how the rendering should be and how the usage could be.

There seems to be coupling with the storage drivers.

To add exemplars in histogram, it needs to ensure that only one exemplar is added per bucket.

Starting by adding public API proposal + Exporter Text format expected output functional test.

[LKaemmerling]

Hey @hrodic,

thank you! This proposal looks fine for me :)