DM-34326 Collect imports in ConfigDictField

[natelust]

This commit fixes an issue where imports for modules were not being
collected from configs owned by a ConfigDictField.

[codecov]

Codecov Report

Merging #69 (eaf871f) into main (6ad3b95) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #69      +/-   ##
==========================================
+ Coverage   83.57%   83.68%   +0.10%     
==========================================
  Files          40       40              
  Lines        2953     2972      +19     
==========================================
+ Hits         2468     2487      +19     
  Misses        485      485              

Impacted Files	Coverage Δ
python/lsst/pex/config/dictField.py	82.22% <ø> (ø)
tests/test_configChoiceField.py	98.83% <ø> (ø)
tests/test_configurableField.py	95.29% <ø> (ø)
tests/test_dictField.py	94.31% <ø> (ø)
tests/test_listField.py	93.20% <ø> (ø)
python/lsst/pex/config/configChoiceField.py	84.98% <100.00%> (+0.05%)	⬆️
python/lsst/pex/config/configDictField.py	87.17% <100.00%> (+0.69%)	⬆️
python/lsst/pex/config/configurableField.py	79.01% <100.00%> (ø)
python/lsst/pex/config/history.py	62.92% <100.00%> (ø)
tests/test_configDictField.py	94.73% <100.00%> (+0.23%)	⬆️
... and 6 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6ad3b95...eaf871f. Read the comment docs.