[metrics-bugs] #22122 [Metrics/metrics-lib]: Add support for six new key-value pairs added by OnionPerf

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#22122: Add support for six new key-value pairs added by OnionPerf
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     Reporter:  karsten              |      Owner:  metrics-team
         Type:  enhancement          |     Status:  new
     Priority:  Medium               |  Milestone:  metrics-lib 1.7.0
    Component:  Metrics/metrics-lib  |    Version:
     Severity:  Normal               |   Keywords:
Actual Points:                       |  Parent ID:
       Points:                       |   Reviewer:
      Sponsor:                       |
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 OnionPerf adds six new key-value pairs to the .tpf format that
 Torperf/CollecTor did not produce: `ENDPOINTLOCAL`, `ENDPOINTPROXY`,
 `ENDPOINTREMOTE`, `HOSTNAMELOCAL`, `HOSTNAMEREMOTE`, and `SOURCEADDRESS`.
 We should add support for these keys to metrics-lib, so that we can start
 using their values.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22122>
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