pg_namespace to disambiguate repeated field name

[mbeynon]

This change fixes the TABLE_COLUMNS_QUERY to work as intended, but using pg_catalog.pg_namespace to disambiguate a case where the same name is used for a custom enum type in more than one schema (namespace) in the database.

Unfixed, this can result in pg_datanymizer building a list of columns with duplicate column names each time the name appears across all the namespaces. The COPY command is rejected by postgres, and the run is aborted.

See issue #148 for more details.

Testable example: (enum event_type defined in 3 namespaces)
schema.dump.txt
test2.yaml.txt

✓ Checklist:

• This PR has been added to CHANGELOG.md (at the top of the list);
• ??? Tests for the changes have been added (for bug fixes / features); UNCLEAR HOW THIS CAN BE TESTED in the code, since it depends on the DB representation.
• Docs have been added / updated (for bug fixes / features).

[codecov-commenter]

Codecov Report

Merging #149 (fd38cdf) into main (f679e34) will decrease coverage by 0.51%.
The diff coverage is n/a.

❗ Current head fd38cdf differs from pull request most recent head 5d2abed. Consider uploading reports for the commit 5d2abed to get more accurate results

@@            Coverage Diff             @@
##             main     #149      +/-   ##
==========================================
- Coverage   86.45%   85.94%   -0.52%     
==========================================
  Files          52       52              
  Lines        3344     3187     -157     
==========================================
- Hits         2891     2739     -152     
+ Misses        453      448       -5     

Impacted Files	Coverage Δ
...atanymizer_dumper/src/postgres/schema_inspector.rs	88.40% <ø> (ø)
datanymizer_engine/src/transformers/datetime.rs	74.07% <0.00%> (-8.86%)	⬇️
datanymizer_dumper/src/postgres/dumper.rs	36.72% <0.00%> (-4.70%)	⬇️
datanymizer_engine/src/settings/filter.rs	96.27% <0.00%> (-2.60%)	⬇️
datanymizer_dumper/src/lib.rs	58.82% <0.00%> (-1.79%)	⬇️
datanymizer_dumper/src/postgres/table.rs	95.36% <0.00%> (+0.05%)	⬆️
datanymizer_engine/src/settings/table.rs	84.37% <0.00%> (+12.50%)	⬆️

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[evgeniy-r]

Hello! Thank you for your contribution. I will take a look.
About testing: we have integration tests, but I can then add a test myself for this case (this may take some time).