Add PPL query language for Observability

[YANG-DB]

Description

Adding PPL query language to the query standards folder including the response for the dsl_survey

Additional Context

• https://github.com/opensearch-project/sql/tree/main/docs/user/ppl
• https://github.com/cncf/tag-observability/blob/main/working-groups/query-standardization/dsl-designer-interview-questions.md