fix: Path issues with pip modules

[tokotchd]

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Always prepend current bentofile directory to system path to avoid unwanted behavior when other bentofiles are on the system PATH This is especially evident when trying to use bentoml cli on python folders that are also pip modules see https://github.com/bentoml/BentoML/issues/4217

[aarnphm]

we probably should note the side effect of doing this here

• If there is a package/folder named grpc, it will override the default grpc import, which makes serve-grpc not working
• the same as schema, or literally any folder that have the same name as package module imports.