Common `build_path` API for on_prem and saas

## Background

Currently, clients need to implement a logic to distinguish between on-prem and SaaS, see [here](https://github.com/exasol/python-extension-common/blob/822762ae0359744a21a6f485bad675fbe281f9d7/exasol/python_extension_common/deployment/language_container_deployer.py#L312). It would be better if the BucketFS API would handle this.