Vector Store Filter Expression does not support boolean types

The filter expression does not support boolean metadata fields.

Consider a document which has following metadata.
`is_active: true
`

I tried various expressions. It does not work.

```
SearchRequest.builder()
             .query(my_query)
             .filterExpression("is_active == true")
             .build()
```

Workaround is to stringify.
`is_active: "true"`
