[migration/pdb] add option to use pdb.post_mortem if traceback is provided
Post mortem is a mode where the pdb shell is opened **where** the exception as
occured instead at the breakpoint for set_trace. This is way more useful for
debugging for the user because is will have the full context of the error.
Closes #17219827
^build$
^dist$
\.egg-info$
^.tox$
^.cache$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
\.pybuild
cubicweb/server/test/data/slapd.conf
debian/python-cubicweb
debian/*.log
debian/*.substvars
debian/cubicweb-doc
debian/cubicweb
debian/files
syntax: regexp
.*/data.*/database/.*
.*/data/ldapdb/.*
.*/data/uicache/
.*/data/libpython/cubicweb_.*/i18n/.*\.po
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
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^doc/js_api/
test-results.xml
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