Use protobuf in gardener components

[timebertt]

How to categorize this issue?

/area performance cost
/kind enhancement
/priority normal

What would you like to be added:
Currently all gardener components are configured to accept and send requests with content type application/json.
We should switch to protobuf (application/vnd.kubernetes.protobuf) by default, where possible.
As we heavily make use of CRDs in our Seed clusters it might not be possible to switch the seed client connection settings to protobuf at all, as CRDs don't support protobuf. But at least for the garden client connection it should be possible.
A fallback to json can be defined for acceptContentTypes with application/vnd.kubernetes.protobuf;application/json.

Why is this needed:
Using protobuf should be more efficient and might safe some data transfer costs.

[timebertt]

This can be partly addressed with #3109 (ref kubernetes-sigs/controller-runtime#1149).
With that we will be able to configure c-r clients to use protobuf for the gardener APIs.

[timebertt]

/assign