migrate keypair resource policy api to sqlalchemy orm partially

[fregataa]

The first step of migration of SQLAlchemy Core API to ORM API. add Declarative KeyPairResourcePolicyRow table which is provided by keypair_resource_policy imperative table. https://docs.sqlalchemy.org/en/14/orm/declarative_tables.html#declarative-with-imperative-table-a-k-a-hybrid-declarative

[fregataa]

I think you just updated the selected column list to be taken from ORM, instead of rewriting SQLAlchemy Core APIs with ORM-based queries. Could we go just one step further?

Note: Since this PR is a small demonstration of the ORM migration changes, let's keep prior table-based queries when the table is accessed from or joined with other querie.

I have a question about keeping prior table-based queries and rewriting SQLAlchemy Core APIs with ORM-based queries. I thought that rewriting Core APIs with ORM-based queries should be like this, therefore there would be no huge change of queries if there is no optimization using sqlalchemy.Session or ORM-based relationships. e.g)

# before
query = sa.select([users]).select_from(users).where(users.c.name == username)

# after
query = sa.select(Users).select_from(Users).where(Users.name == username)

am I misunderstanding between migrating to 2.0 and rewriting with ORM-based queries?