Show buildkit version as a component in nerdctl version

[afbjorklund]

What is the problem you're trying to solve

Currently the version of containerd is shown, but not the version of buildkit.

Server:
 containerd:
  Version:	1.5.9-0ubuntu1~20.04.4
  GitCommit:	

Describe the solution you'd like

I would like to see the buildkit version, where available (not everywhere)

Server:
 containerd:
  Version:	v1.5.11
  GitCommit:	3df54a852345ae127d1fa3092b95168e4a88e2f8
 buildkit:
  Version:	v0.9.3
  GitCommit:	8d2625494a6a3d413e3d875a2ff7dd9b1ed1b1a9

Additional context

It seems like nerdctl is currently showing the client version of containerd ?

ctr version (output matches the Client, rather than the Server, version)

That means it would be easier to implement, to show the buildctl version

buildctl --version (doesn't require setting up the buildkit socket and all)

If wanting to show the server version of buildkit, it needs the new feature:

buildctl debug info (returns a "BuildKit:" component, similar to "buildctl")

[afbjorklund]

This is now implemented (since 0.22.0), showing the client version:

Client:
 Version:	v0.23.0
 OS/Arch:	linux/amd64
 Git commit:	660680b7ddfde1d38a66ec1c7f08f8d89ab92c68
 buildctl:
  Version:	v0.9.3
  GitCommit:	8d2625494a6a3d413e3d875a2ff7dd9b1ed1b1a9

Server:
 containerd:
  Version:	v1.6.1
  GitCommit:	10f428dac7cec44c864e1b830a4623af27a9fc70
 runc:
  Version:	1.1.0-0ubuntu1~20.04.1