[PPL] Vega support with PPL

[YANG-DB]

Is your feature request related to a problem?
As a vega visualization user, I'd like to be able to query OpenSearch using PPL query language.

What solution would you like?
OpenSearch provide multiple query languages endpoint to fetch data. Vega visualization currently only supports DQL language
I'd like to be able to use vega visualization with the PPL language and allow the PPL capability for federating queries for other datasources into the visualization itself.

Suggested vega PPL query:

 "data": {
  "url" :{
      "%context%": "true",
      "%timefield%": "startTime",
      "index": "otel-v1-apm-span-*",
      "query": "source = %index% | stats sum(productsAmount) by span(transactionDate, 1d) as age_date | sort age_date"
    }
    "format":{
      "type": "json",
      "property":"hits.hits"
    }
  },

What alternatives have you considered?
A clear and concise description of any alternative solutions or features you've considered.

Do you have any additional context?
#5927

• https://opensearch.org/docs/latest/dashboards/visualize/viz-index/#vega
• https://github.com/opensearch-project/OpenSearch-Dashboards/tree/e08bf3059896449d2c008059c47b0b3de8da8c9e/src/plugins/vis_type_vega

[ashwin-pc]

Since PPL isnt supported in a minimal distribution of OpenSearch, we need to make sure that this extension is more generic so that a plugin can bring in their own queries. We shouldnt take a dependency on something that isnt part of the core

[YANG-DB]

PPL is moving inside the core API capabilities so this becomes redundant