📚 Fix pyexasol connection documentation for SaaS

[tkilias]

Summary

Currently, we describe in the documentation that you need OpenID to connect SaaS. For a while, you only need your username and personal access token to connect to the DB.

References

• https://docs.exasol.com/db/latest/sql/create_user.htm#Authenti4
• https://docs.exasol.com/saas/administration/access_mngt/access_token.htm
• https://docs.exasol.com/saas/administration/access_mngt/access_management.htm?Highlight=OpenID

Task(s)

• Mention that OpenID is still a possibility, but not always needed.
• Add mention that you need only username and password for SaaS.