refactor(ingest): streamline two-tier db config validation

[hsheth2]

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub

[github-actions]

Unit Test Results (metadata ingestion)

       8 files  ±0         8 suites  ±0   58m 25s ⏱️ +47s
   717 tests ±0     714 ✔️ ±0  3 💤 ±0  0 ❌ ±0 
1 436 runs  ±0  1 430 ✔️ ±0  6 💤 ±0  0 ❌ ±0 

Results for commit ad99a50. ± Comparison against base commit b195b6c1.

This pull request removes 2 and adds 2 tests. Note that renamed tests count towards both.

tests.integration.tableau.test_tableau ‑ test_lineage_overrides
tests.integration.tableau.test_tableau ‑ test_tableau_ingest

tests.integration.tableau.test_tableau_ingest ‑ test_lineage_overrides
tests.integration.tableau.test_tableau_ingest ‑ test_tableau_ingest

♻️ This comment has been updated with latest results.

[github-actions]

Unit Test Results (build & test)

562 tests  +74   562 ✔️ +74   13m 20s ⏱️ + 1m 35s
139 suites +25       0 💤 ±  0 
139 files   +25       0 ❌ ±  0 

Results for commit ad99a50. ± Comparison against base commit b195b6c1.

♻️ This comment has been updated with latest results.

[rslanka]

LGTM! Do we already have unit tests that cover this code path?