Relock transitive dependencies

[ArBridgeman]

Summary

• Our transitive dependency urllib3 has a vulnerability, so let's relock:
  https://github.com/exasol/sqlalchemy-exasol/security/dependabot/52
• Widen PyExasol as version 2.0.0 compatible with current SQLA
• Make main dependencies & project sections PEP-compliant