obsmarker: track operation by default We added support for including the operation responsible for creating the obsmarker in 3546a771e376 (obsolete: add operation metadata to rebase/amend/histedit obsmarkers, 2017-05-09). However, soon thereafter, in f432897a9f49 (obsmarker: add an experimental flag controlling "operation" recording, 2017-05-20), it was hidden behind a config that was off by default. It seems unlikely that people will manually turn it on, and obsmarkers/evolution as a whole is still experimental anyway, so let's turn on the tracking by default. Differential Revision: https://phab.mercurial-scm.org/D722