Add/Implement pytest plugin

[Nicoretti]

Summary

In order to easily use the ITDE capabilities within pytest based test, provide a pytest plugin which then can be used by/in other projects.

As a starting point parts of https://github.com/exasol/sqlalchemy-exasol/blob/master/test/integration/conftest.py could be used.

At least the following things should be supported:

• Reading and configuring DB configuration parameters (DSN, username, password, ...)
• session fixture to setup (start/stop) a DB
• fixture providing a control connection to prepare change things in db apart from the test itself