SparkSQL: Support for CONVERT TO DELTA command

[R7L208]

Brief summary of the change made

• update PartitionSpecGrammar to allow ColumnDefinitionSegment as a valid segment
• add ICEBERG non-reserved keyword
• add ConvertToDeltaStatementSegment class
• test cases

Are there any other side effects of this change that we should be aware of?

N/A

Pull Request checklist

• Please confirm you have completed any of the necessary steps below.

• Included test cases to demonstrate any code changes, which may be one or more of the following:

  • .yml rule test cases in test/fixtures/rules/std_rule_cases.
  • .sql/.yml parser test cases in test/fixtures/dialects (note YML files can be auto generated with tox -e generate-fixture-yml).
  • Full autofix test cases in test/fixtures/linter/autofix.
  • Other.

• Added appropriate documentation for the change.

• Created GitHub issues for any relevant followup/future enhancements if appropriate.

[codecov]

Codecov Report

Merging #3482 (b3dce88) into main (9ec9acd) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main     #3482   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          171       171           
  Lines        12979     12982    +3     
=========================================
+ Hits         12979     12982    +3     

Impacted Files	Coverage Δ
src/sqlfluff/dialects/dialect_sparksql_keywords.py	100.00% <ø> (ø)
src/sqlfluff/dialects/dialect_sparksql.py	100.00% <100.00%> (ø)

---

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 9ec9acd...b3dce88. Read the comment docs.

[tunetheweb]

LGTM with one nit.