Adhere to the MacOS File System Programming Guide

The user's home directory is not the place to dump program data, and for future cross-platform compatibility handling this would be inappropriate. Currently Ollama stores user data in `~/.ollama`, however Apple have a specification for where to place files of various types ([link](https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/FileSystemOverview/FileSystemOverview.html#//apple_ref/doc/uid/TP40010672-CH2-SW1)). In Ollama's case, `~/Library/Application Support/Ollama` seems appropriate.