Translate PPL LOOKUP Command

[LantaoJin]

Description

Syntax

| LOOKUP <lookupIndex> (<lookupMappingField> [AS <sourceMappingField>])...
   [(APPEND | REPLACE) (<lookupOutputField> [AS sourceOutputField])...]

The field name starting with "lookup" means the field is from lookupIndex
The field name starting with "source" means the field is from sourceIndex

Issues Resolved

Resolves #620 and parent issue opensearch-project/sql#2651

Check List

• Updated documentation (ppl-spark-integration/README.md)
• Implemented unit tests
• Implemented tests for combination with other commands
• Commits are signed per the DCO using --signoff

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