Enhancement: separate RepositoryService method for `SELECT FOR UPDATE`

[funkindy]

Summary

In have some default transactions with steps:

1. Get row from database and lock it with FOR UPDATE
2. Check/validate row data
3. Update row

I cant find a good way for step 1 except providing the statement like this:

await repo.get(
    item_id=item_id,
    id_attribute='id',
    statement=select(Item).with_for_update(),
)

This is inconsistent with update/upsert/... RepositoryService API, which provide convenient with_for_update argument.

Maybe consider adding this argument for get* RepositoryService API?

Pure SA Session.get method includes this argument as well: https://docs.sqlalchemy.org/en/20/orm/session_api.html#sqlalchemy.orm.Session.get