QA: Add EOL/deprecation warning about support for SQLAlchemy 1.3

[amotl]

Introduction

We decided to drop support for SQLAlchemy 1.3 within one of the upcoming releases and are tracking this at crate/sqlalchemy-cratedb#85.

About

This patch adds a corresponding EOL/deprecation warning to the package, which will be emitted at runtime when running the Python interpreter with default warnings enabled ¹².

python -Wd -c "import crate.client.sqlalchemy"
PYTHONWARNINGS=default python -c "import crate.client.sqlalchemy"

/path/to/crate/client/sqlalchemy/__init__.py:38: DeprecationWarning: WARNING: SQLAlchemy 1.3 is effectively EOL.
With SQLAlchemy 2 around the corner, this will be even more immanent.
Future versions of the CrateDB SQLAlchemy dialect will drop support for SQLAlchemy 1.3.
It is recommended that you transition to using SQLAlchemy 1.4 or 2.0.

Footnotes

1. https://docs.python.org/3/library/warnings.html#updating-code-for-new-versions-of-dependencies ↩

2. https://docs.python.org/3/using/cmdline.html#cmdoption-W ↩

[hlcianfagna]

@amotl please check if the change I made on 2913ca9 makes sense

[hammerhead]

2.0 was released stable last night, and 1.3 is now officially EOL as per the "release status" table on https://www.sqlalchemy.org/download.html.

[amotl]

Thanks. I've adjusted the admonition text correspondingly, and asked you and @hlcianfagna for another review. Thanks in advance!