feat: Allow gcs paths without prefix

[project-defiant]

Context

I want to use google cloud storage paths that do not have prefix like gs://gwas_catalog_data/manifests/ with the GCSPath object. This will be required for data relocation within the genetics_etl dag.

Currently GCSPath object regex requires path to have prefix and filename groups which prevents us from using paths without the prefix, or paths that point directly to the directories within this class.

Implementation

This PR tries to solve it by changing the regex pattern to catch path instead of filename and prefix and extract the logic behind pathfilename and prefix parsing to the GCSPath.segments method.

• Refactored POSIX_PATH_PATTERN to capture path instead of prefix and filename.
• Refactored GCSPath.segments and GCSPath.path methods to preserve backwards compatibility.
• Added tests for GCSPath object.

[javfg]

Looks good!