Introduce environment variable to provide path to file storage of backend

[dominikriemer]

Body

Currently, icons, files and documentation is stored in a fixed folder in the backend (user.home/.streampipes). In some scenarios (e.g., when running the backend Docker container as a custom/non-root user), it might be necessary to manually provide the folder for storing assets and files.

This should be done by introducing a new environment variable SP_CORE_ASSET_BASE_DIR.

StreamPipes Committer

I acknowledge that I am a maintainer/committer of the Apache StreamPipes project.