Support match_bool_prefix function in SQL/PPL query engine

[chloe-zh]

Related design is presented in issue #182

Todo list

• Support the match_bool_prefix functionality by pushing it down to the search engine
• Enable match_bool_prefix function in SQL and PPL syntax and parser, including all the available parameters
• Add unit tests. (Unit tests are mandatory for all code changes.)
• Add integration test cases for match_bool_prefix
• Update user manual

Function details

The match_bool_prefix function maps to the match bool prefix query in the search engine. This query analyzes its input and constructs a bool query from the terms. Each term except the last is used in a term query. The last term is used in a prefix query.

Syntax:
match_phrase_prefix(field_expression, query_expression[, option=<option_value>]*)

Available options:

• minimum_should_match
• fuziness
• prefix_length
• max_expansions
• fuzzy_transpositions
• fuzzy_rewrite

Sample queries:

# Search query 
GET my_index/_search
{
  "query": {
    "match_bool_prefix": {
      "message": {
        "query": "quick brown f",
        "analyzer": "keyword"
      }
    }
  }
}

# SQL
SELECT * FROM my_index WHERE match_bool_prefix(message, "quick brown f", analyzer="keyword")

# PPL
source=my_index | where match_bool_prefix(message, "quick brown f", analyzer="keyword")