Use JSONB for serialized_dag data column in PostgreSQL

[kaxil]

Improves storage efficiency and query performance for DAG serialization data by using PostgreSQL's native JSONB type instead of JSON. JSONB provides better compression, faster equality comparisons, and removes whitespace/duplicate keys. Would have also made the query in #55975 simpler.

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[ashb]

airflow-core/tests/unit/cli/commands/test_dag_command.py::TestCliDags::test_show_dag_dependencies_save - sqlalchemy.exc.ProgrammingError: (psycopg2.errors.UndefinedFunction) function json_extract_path(jsonb, unknown, unknown) does not exist

That's now failing because we are using json_extract_path on a jsonb type. However I'm not even sure we need that function and custom type -- can't we use the json ops in sqla (even 1.4 had this): https://docs.sqlalchemy.org/en/14/core/type_basics.html#:~:text=path%20index%20operations

data_table.c.data[('key_1', 'key_2', 5, ..., 'key_n')]

The postgres docs say that this:

Extracts JSON sub-object at the specified path. (This is functionally equivalent to the #> operator, but writing the path out as a variadic list can be more convenient in some cases.)

In [36]: metadata = MetaData()

In [37]: data_table = Table('data_table', metadata,
    ...:     Column('id', Integer, primary_key=True),
    ...:     Column('data', JSONB)
    ...: )

In [38]: clause = select(data_table.c.data[('key_1', 'key_2', 5, 'key_n')])

In [39]: str(clause.compile(dialect=_25, compile_kwargs={"literal_binds": True}))
Out[39]: "SELECT data_table.data #> '{key_1, key_2, 5, key_n}' AS anon_1 \nFROM data_table"

Edit: ah the custom type is in HITL model