[metrics-bugs] #33433 [Metrics/Onionperf]: Add error handling for older stem versions

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#33433: Add error handling for older stem versions
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     Reporter:  acute              |      Owner:  metrics-team
         Type:  defect             |     Status:  new
     Priority:  Medium             |  Milestone:
    Component:  Metrics/Onionperf  |    Version:
     Severity:  Normal             |   Keywords:
Actual Points:                     |  Parent ID:
       Points:                     |   Reviewer:
      Sponsor:                     |
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 Currently OP fails if the python-stem version required for enabling v3
 services is not found. Instead, it should warn the user and either
 continue with v2 services only, or exit and ask the user to manually
 exclude v3 services on the command line.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33433>
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