fix(workflow-operator): default boolean metadata fields

[officialasishkumar]

What changes were proposed in this PR?

Some operator boolean properties initialized to false did not declare a JSON-schema default value, so the frontend form could render them as neutral checkboxes instead of unchecked checkboxes.

This PR adds explicit defaultValue = "false" metadata for:

• FilledAreaPlotOpDesc.facetColumn
• DumbbellPlotOpDesc.showLegends
• JSONLScanSourceOpDesc.flatten

It also adds a focused metadata-generation spec that asserts these boolean schemas include a false default.

Any related issues, documentation, discussions?

Closes #4015.

How was this PR tested?

Validated locally with a temporary Postgres container loaded with the same DDL files used by CI for JOOQ generation.

JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64 COURSIER_CACHE=/tmp/texera-coursier-cache /usr/lib/jvm/java-17-openjdk-amd64/bin/java -Dsbt.ivy.home=/tmp/texera-ivy-cache -Dsbt.boot.directory=/tmp/texera-sbt-boot -Dsbt.global.base=/tmp/texera-sbt-global -jar /tmp/sbt-launch-1.12.9.jar "WorkflowOperator/testOnly org.apache.texera.amber.operator.metadata.OperatorBooleanDefaultSpec"

Result: 2 passed.

JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64 COURSIER_CACHE=/tmp/texera-coursier-cache /usr/lib/jvm/java-17-openjdk-amd64/bin/java -Dsbt.ivy.home=/tmp/texera-ivy-cache -Dsbt.boot.directory=/tmp/texera-sbt-boot -Dsbt.global.base=/tmp/texera-sbt-global -jar /tmp/sbt-launch-1.12.9.jar scalafmtCheckAll

Result: passed.

Was this PR authored or co-authored using generative AI tooling?

Generated-by: OpenAI Codex (GPT-5)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.26%. Comparing base (e7e5d4e) to head (f837f4b).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5177      +/-   ##
============================================
+ Coverage     43.65%   46.26%   +2.61%     
- Complexity     2219     2369     +150     
============================================
  Files          1049     1049              
  Lines         40572    40572              
  Branches       4324     4324              
============================================
+ Hits          17713    18772    +1059     
+ Misses        21767    20657    -1110     
- Partials       1092     1143      +51     

Flag	Coverage Δ		*Carryforward flag
access-control-service	39.53% <ø> (ø)
agent-service	33.76% <ø> (ø)		Carriedforward from e7e5d4e
amber	50.79% <ø> (+6.74%)	⬆️
computing-unit-managing-service	0.00% <ø> (ø)
config-service	0.00% <ø> (ø)
file-service	32.18% <ø> (ø)
frontend	35.15% <ø> (ø)		Carriedforward from e7e5d4e
python	90.50% <ø> (ø)		Carriedforward from e7e5d4e
workflow-compiling-service	56.81% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

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[Yicong-Huang]

LGTM. Thanks for the fix!