[MacPorts] #70291: Add portimage_mode to macports.conf on APFS builders

[MacPorts]

#70291: Add portimage_mode to macports.conf on APFS builders
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 Reporter:  jmroot         |      Owner:  admin@…
     Type:  enhancement    |     Status:  new
 Priority:  Normal         |  Milestone:
Component:  buildbot/mpbb  |    Version:
 Keywords:                 |       Port:
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 This will enable the performance improvements of #69555 for ports that are
 activated more than once. We could either use `portimage_mode directory`
 and build the archive from the image directory during the gather_archives
 step, or use `portimage_mode directory_and_archive` and delete the archive
 after uploading. The latter may have the drawback of keeping around
 unnecessary archives for ports that have already had their archive
 deployed and are installed later as a dependency, unless we add code to
 delete the archives in that situation.

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Ticket URL: <https://trac.macports.org/ticket/70291>
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