Use poetry for dependency management

[dclimber]

Whilst installing dependencies I have stumbled upon the following conflicts:

1. Python 3.6
   • current Python requirement (>=3.6,<4.0) is not compatible with tortoise-orm's requirement of Python >=3.7,<4.0.
2. ormar and gino-starlette have conflicting importlib_metadata version requirements.
3. databases and gino-starlette have conflicting requirements for SQLAlchemy.
4. pytest >= 7 has conflicting requirements.

My proposal — use poetry for managing dependencies:

• it automatically resolves issues with dependencies;
• no need for creating virtual environment manually — poetry creates it for you;
• there are some other advantages.

Haven't seen any open/closed issues or pull requests on the subject, so opening this ticket.

[dclimber]

Another dependency conflict:

• gino-starlette (0.1.4) depends on gino (>=1.0.1,<2.0.0)
• gino (1.0.1) depends on importlib_metadata (>=1.3.0,<2.0.0
• ormar (0.10.24) depends on importlib-metadata (>=3.1)

Downgrading ormar to 0.9.4 solves the above conflict, but causes this issue, which was resolved in ormar (0.10.24)

[dclimber]

1. Downgraded several dependencies, now pytest's tests pass locally on my python 3.8 machine.
2. Support for python 3.6 had to be removed, due to tortoise-orm 0.17.8 not supporting it.
   • pipelines were also updated — now they are 3.7 and higher.