DM-45668: Add --namespace option to ap_verify command line

[andy-slac]

The --namespace option can be used together with --db option to run ap_verify against a shared postgres database.

{Summary of changes. Prefix PR title with JIRA issue.}

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• Do unit tests pass (scons and/or stack-os-matrix)?
• Did you run ap_verify.py on at least one of the standard datasets?
  For changes to metrics, the print_metricvalues script from lsst.verify will be useful.
• Is the Sphinx documentation up-to-date?

[kfindeisen]

Absolutely rejected. ap_verify has a single purpose -- to run standardized datasets, in a self-contained environment, in a reproducible manner. Neither I nor anyone else has the time to maintain the gold-plating of trying to turn it into a general-purpose execution framework; that's what pipetask run is for.

[andy-slac]

OK, no problem, it was useful to me to run it in standalone, as I do not know how to run pipetask (and I don't have data on my test machine). Will cancel this PR.