replace deprecated stpipe configobj with astropy

[braingram]

configobj use from stpipe is deprecated. This is causing warnings in test runs:

  /home/runner/work/romancal/romancal/.tox/py311-ddtrace-webbpsf/lib/python3.11/site-packages/ddtrace/internal/module.py:220: DeprecationWarning: stpipe.extern.configobj is deprecated in favor of astropy.extern.configobj, please use that instead.

This PR uses configobj from astropy similar to what is done in jwst.

With this PR the warning is no longer seen in the test runs: https://github.com/spacetelescope/romancal/actions/runs/9418970328/job/25947683547?pr=1267#step:10:260

Checklist

• [ ] added entry in CHANGES.rst under the corresponding subsection
• [ ] updated relevant tests
• [ ] updated relevant documentation
• [ ] updated relevant milestone(s)
• [ ] added relevant label(s)
• [ ] ran regression tests, post a link to the Jenkins job below. How to run regression tests on a PR

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 79.30%. Comparing base (bcfdb71) to head (fd65240).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1267 +/- ## ======================================= Coverage 79.30% 79.30% ======================================= Files 117 117 Lines 8065 8065 ======================================= Hits 6396 6396 Misses 1669 1669 ``` | [Flag](https://app.codecov.io/gh/spacetelescope/romancal/pull/1267/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) | Coverage Δ | | *Carryforward flag | |---|---|---|---| | [nightly](https://app.codecov.io/gh/spacetelescope/romancal/pull/1267/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) | `62.78% <ø> (ø)` | | Carriedforward from [bcfdb71](https://app.codecov.io/gh/spacetelescope/romancal/commit/bcfdb7183bbc82bf1e4955bd24658201b71b59ad?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) | *This pull request uses carry forward flags. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.