feat: Built-in hybrid search

[gaocegege]

We need to design how to support hybrid search, including but not limited to:

• Rerank
• Full-text support
• A function to get the ranking score of results

-- create table

CREATE TABLE items (
  id bigserial PRIMARY KEY,
  content TEXT NOT NULL
);

INSERT INTO items (embedding)
VALUES ('pgvecto.rs is a ...');

-- Some logics to configure the hybrid search (a.k.a hs), then:

SELECT * FROM items ORDER BY content hs-op 'what is pgvecto.rs' LIMIT 5;