[FEATURE] Support PPL language through customizable search strategy

[joshuali925]

Is your feature request related to a problem?

In OpenSearch Dashboards there can be datasource types that do not support DSL, such as S3. Currently the maps are built using DSL queries, this makes them not usable with those datasource types.

What solution would you like?

Support PPL language through PPL search strategy defined by core (code)

data.search.registerSearchStrategy(SEARCH_STRATEGY.PPL, pplSearchStrategy);

Discover currently calls the search strategy defined by the datasource type, for example (code)

  public search(request: IOpenSearchDashboardsSearchRequest, options: ISearchOptions) {
    const dataset = this.queryService.queryString.getQuery().dataset;
    const datasetType = dataset?.type;
    let strategy = datasetType === DATASET.S3 ? SEARCH_STRATEGY.PPL_ASYNC : SEARCH_STRATEGY.PPL;

It would be good for maps to also support search through search strategy, and we can send queries in PPL to support maps using datasources that do not support DSL.

What alternatives have you considered?

Add DSL support to all datasources, but this is not very feasible because they may not be stored in OpenSearch.

Do you have any additional context?

There are open-ended areas like PPL does not support all aggregations used by maps, and how to correctly map the UI configuration to PPL query.

[krisfreedain]

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