[MacPorts] #64369: Add fetch.user_agent

[MacPorts]

#64369: Add fetch.user_agent
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 Reporter:  ryandesign   |      Owner:  (none)
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  base         |    Version:  2.7.1
 Keywords:               |       Port:
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 MacPorts supports setting `fetch.user_agent` for stupid servers that
 disallow access from curl. This same condition can easily prevent
 livecheck from working. There should be a `livecheck.user_agent` option.

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Ticket URL: <https://trac.macports.org/ticket/64369>
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