[FEATURE]Move PPL AST (SQL) and consolidate

[YANG-DB]

Is your feature request related to a problem?

This second step of consolidating the PPL spec into a single repository which will be deployed as an independent artifact.

What solution would you like?

Second step:

• Move PPL AST visitors into this repo
• consolidate different divergence between SQL's & Spark's PPL AST
• add as a jar artifact publishing to Maven

#23 - Main RFC

Do you have any additional context?

• https://github.com/opensearch-project/sql/tree/main/ppl/src/main/antlr
• https://github.com/opensearch-project/sql/tree/main/ppl/src/main/java/org/opensearch/sql/ppl
• https://github.com/opensearch-project/opensearch-spark/tree/main/ppl-spark-integration/src/main/java/org/opensearch/sql/ast
• https://github.com/opensearch-project/opensearch-spark/tree/main/ppl-spark-integration/src/main/antlr4