Add JSONObject Func

[Chiorufarewerin]

So I currently use for build json object for postgres like:

Func(
    Value('name'), 'authors__name',
    Value('alias'), 'authors__alias',
    function='jsonb_build_object'
)

I checked other dbs formats for this, and all of this have that functional:
​https://www.sqlite.org/json1.html#jobj
​https://dev.mysql.com/doc/refman/8.0/en/json-creation-functions.html#function_json-object
​https://docs.oracle.com/en/database/oracle/oracle-database/12.2/sqlrf/JSON_OBJECT.html

I use it for related objects, for example:

class Article(models.Model):
    title = models.CharField(max_length=50)


class Product(models.Model):
    article = models.ForeignKey(Article, related_name='products', on_delete=models.CASCADE)
    name = models.CharField(max_length=255)

Product.objects.annotate(
    article_json=Func(
        Value('title'), 'article__title',
        function='JSONB_BUILD_OBJECT',
    )
).values('name', 'article_json').first()

So, with JSONObject will be something like this:

Product.objects.annotate(
    article_json=JSONObject(
        title='article__title',
    )
).values('name', 'article_json').first()

[Mariusz Felisiak <felisiak.mariusz@…>]

In 48b4bae9:

Fixed #32179 -- Added JSONObject database function.