fix: Improve error message for metadata conflict in schema

[mkleen]

Which issue does this PR close?

• Closes Join swap in join_selection flips schema-level metadata, failing "Schema mismatch" #23461

Rationale for this change

Based on the discussion in #23461 this pr improves the error message when there is a metadata conflict when schemas get merged. It also reverts #23605, so CrossJoinExec has again it's original behavior.

select * from larger_table cross join smaller_table;

DataFusion error: PhysicalOptimizer rule 'join_selection' failed. Schema mismatch caused by 
Internal error: Schema metadata mismatch: Expected original metadata: {"metadata_key": "right"}, got metadata: {"metadata_key": "left"}

What changes are included in this PR?

• Revert fix: Preserve metadata when a cross-join is swapped #23605 the behavior change for CrossJoinExec
• Improve error messages for schema validation in physical_planner.rs
• Data creation in test_context.rs
• Reproduction in metadata.slt

Are these changes tested?

Yes

Are there any user-facing changes?

Yes, error message improved when the schema metadata has conflicting keys using a cross-join.