Fix 'itsdangerous' import error when not using Authentication Backend

[GriceTurrble]

Issue

When importing sqladmin.Admin:

from sqladmin import Admin

...the application imports from .authentication:

sqladmin/sqladmin/application.py

Line 34 in 724b9a9

from sqladmin.authentication import AuthenticationBackend, login_required

Which in turn calls starlette.middleware.sessions:

sqladmin/sqladmin/authentication.py

Line 6 in 724b9a9

from starlette.middleware.sessions import SessionMiddleware

And in starlette package, middleware.session tries to import itsdangerous: https://github.com/encode/starlette/blob/cb6d284877cd359a21a0f31ebf8103a7b285a848/starlette/middleware/sessions.py#L5

However, this package is not installed automatically: it's part of the "full" deps: https://github.com/encode/starlette/blob/cb6d284877cd359a21a0f31ebf8103a7b285a848/pyproject.toml#L37

Therefore, it's easily possible to install sqladmin and not this crucial sub-dependency, creating an error when trying to run the site:

Solution

Either:

1. Mark itsdangerous as a named dependency here (which seems odd to name a sub-dependency just to alleviate this issue); or
2. Install starlette[full] as a main dependency, ensuring all dependencies are covered up front.

This PR is a simple change implementing the latter.

[aminalaee]

Thanks for the PR, I had missed this for a long time.

[aminalaee]

Thanks for the fix 👍