Refactor span log helpers

[aledbf]

Dropped 183 nodes (cum <= 3.61MB)
Showing top 10 nodes out of 25
      flat  flat%   sum%        cum   cum%
  318.73MB 44.16% 44.16%   318.73MB 44.16%  github.com/uber/jaeger-client-go.(*Span).appendLogNoLocking (inline)
  192.51MB 26.67% 70.83%   486.61MB 67.41%  github.com/gitpod-io/gitpod/common-go/tracing.LogEvent (inline)
  184.01MB 25.49% 96.32%   208.64MB 28.90%  github.com/gitpod-io/gitpod/common-go/tracing.LogKV (inline)
    1.50MB  0.21% 96.53%     4.02MB  0.56%  k8s.io/api/core/v1.(*Container).Unmarshal
         0     0% 96.53%   695.26MB 96.32%  github.com/gitpod-io/gitpod/ws-manager/pkg/manager.(*Monitor).actOnPodEvent.func2
         0     0% 96.53%   695.26MB 96.32%  github.com/gitpod-io/gitpod/ws-manager/pkg/manager.(*Monitor).probeWorkspaceReady
         0     0% 96.53%   695.26MB 96.32%  github.com/gitpod-io/gitpod/ws-manager/pkg/manager.(*Monitor).waitForWorkspaceReady
         0     0% 96.53%   695.26MB 96.32%  github.com/gitpod-io/gitpod/ws-manager/pkg/manager.(*WorkspaceReadyProbe).Run
         0     0% 96.53%    10.27MB  1.42%  github.com/gogo/protobuf/proto.Unmarshal
         0     0% 96.53%   318.73MB 44.16%  github.com/uber/jaeger-client-go.(*Span).LogFields

xref: #4106