Feature/configurable oracle package (#21)

* Support for cx_oracle and oracledb

* Fixing connection helper

* Adding documentation

* Supporting SQLNET_ORA_CONFIG config

* Adding MacOS support

* isort imports and support env overrides of driver

* Correct MacOS ORA_PYTHON_DRIVER_TYPE=thin setting

* Pointing to correct dictionary

* Fixing documentation for SQLNET.ora thin config

* Adding some more documentation

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Co-authored-by: Steve Clarke <stephen.clarke@health.govt.nz>