chore: move proto to sdk conversion to agentsdk (#11831)

`agentsdk` depends on `agent/proto` because it needs to get the version to dial.

Therefore, the conversion routines need to live in `agentsdk` so that we can convert to and from the Manifest.

I briefly considered refactoring the agent to only reference `proto.Manifest`, but decided against it because we might have multiple protocol versions in the future, its useful to have a protocol-independent data structure.

coderd/agentapi/servicebanner.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/coder/coder/v2/agent/proto"
 	"github.com/coder/coder/v2/coderd/appearance"
+	"github.com/coder/coder/v2/codersdk/agentsdk"
 )
 
 type ServiceBannerAPI struct {
@@ -19,5 +20,5 @@ func (a *ServiceBannerAPI) GetServiceBanner(ctx context.Context, _ *proto.GetSer
 	if err != nil {
 		return nil, xerrors.Errorf("fetch appearance: %w", err)
 	}
-	return proto.ServiceBannerFromSDK(cfg.ServiceBanner), nil
+	return agentsdk.ProtoFromServiceBanner(cfg.ServiceBanner), nil
 }