add progress bars to the VM importer
The new progress bars supposed to display the processing speed per each
VM importer worker. This info should help to identify if there is a bottleneck
on the VM side during the import process, without waiting for its finish.
The new progress bars can be disabled by passing `vm-disable-progress-bar` flag.
Plotting multiple progress bars requires using experimental progress bar pool
from github.com/cheggaaa/pb/v3. Switch to progress bar pool required changes
in all import modes.
The openTSDB mode wasn't changed due to its implementation, which implies individual progress
bars per each series. Because of this, using the pool wasn't possible.
Signed-off-by: dmitryk-dk <kozlovdmitriyy@gmail.com>
Co-authored-by: hagen1778 <roman@victoriametrics.com>
