Support partial match in PPL

[prashanttct07]

Is your feature request related to a problem? Please describe.
PPL does not allow to run partial search, something like an equivalent of query-string or match query.
Consider I have a document with as "title":"learning opensearch is fun"
Now if I want to get all the document where "fun" is present, as of now there is no way to run this kind of filter. And I need to run search source=my_index | where title="learning opensearch is fun"

Describe the solution you'd like
I would like the PPL to run query something like:
search source=my_index | where title="fun" or search source=my_index | where title="*fun*"
And above query would get me if it matches the document with partial data on title.

Describe alternatives you've considered
Instead of using PPL, I am using regular GET API with query_string/match query

[anirudha]

thanks pls review #182

[dai-chen]

@prashanttct07 Thanks for reporting the issue! The full text search function you mentioned is already supported in PPL. Please check out https://github.com/opensearch-project/sql/blob/main/docs/user/ppl/functions/relevance.rst