fix(puller): fixes related to an empty model path

[tjohnson31415]

Motivation

Removes some buggy behavior related to the handling of an empty modelPath being passed into the puller

Modifications

• use filepath.Join() instead of manual string concatenation with the file separator to handle an empty modelPathFilename
• in the http storageProvider, remove duplication of the localPath into the rendered path
  • just to not it: I think this bug has not been caught because using the HTTP provider with a storageURI means that the local path is empty
    • this will need to be fixed before https://github.com/kserve/modelmesh-serving/pull/382 can be merged
• add check to ensure that the local path for files downloaded by the puller is always a path within the generated model dir (prevents the generated dir name from being the model file as was seen in https://github.com/kserve/modelmesh-runtime-adapter/issues/41#issuecomment-1564909111)
  • if no path is extracted from the request ModelPath, use _model by default

Result

Resolves: https://github.com/kserve/modelmesh-runtime-adapter/issues/41

[kserve-oss-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ckadner, tjohnson31415

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