Update requirements.txt for SqlAlchemy

[kazyakj]

Related to Issue 41
With the release of SqlAlchemy2 the sqlalchemy.orm.mapper() was removed completely. This causes the cosmicpython-redis_pubsub-1 and cosmicpython-api-1 containers to fail.

Traceback (most recent call last):
  File "/src/allocation/entrypoints/redis_eventconsumer.py", line 31, in <module>
    main()
  File "/src/allocation/entrypoints/redis_eventconsumer.py", line 15, in main
    bus = bootstrap.bootstrap()
  File "/src/allocation/bootstrap.py", line 22, in bootstrap
    orm.start_mappers()
  File "/src/allocation/adapters/orm.py", line 65, in start_mappers
    lines_mapper = mapper(model.OrderLine, order_lines)
  File "/usr/local/lib/python3.9/site-packages/sqlalchemy/orm/_orm_constructors.py", line 1880, in _mapper_fn
    raise InvalidRequestError(
sqlalchemy.exc.InvalidRequestError: The 'sqlalchemy.orm.mapper()' function is removed as of SQLAlchemy 2.0.  

Use the 'sqlalchemy.orm.registry.map_imperatively()` method of the ``sqlalchemy.orm.registry`` class to perform classical mapping.

Not sure what the status of PR 44 is but as a quick fix simply specifying an explicit SqlAlchemy version in the requirements.txt allows the containers to build successfully without requiring any code changes.

sqlalchemy -> sqlalchemy~=1.4.46 

[ljak]

Validating the version.

[hjwp]

hey i think i already hacked in a fix for this with sqlalchemy<2

must get round to upgrading someday!

thanks in any case, hope you've enjoyed the book!