Centralize server config handling

[dhiltgen]

This moves all the env var reading into one central module and logs the loaded config once at startup which should help in troubleshooting user server logs

Example server output

% ollama serve 2>&1 | head -1
2024/05/05 14:56:27 routes.go:989: INFO server config env="map[OLLAMA_DEBUG:false OLLAMA_LLM_LIBRARY: OLLAMA_MAX_LOADED_MODELS:1 OLLAMA_MAX_VRAM:0 OLLAMA_NOPRUNE:false OLLAMA_NUM_PARALLEL:1 OLLAMA_ORIGINS:[http://localhost https://localhost http://localhost:* https://localhost:* http://127.0.0.1 https://127.0.0.1 http://127.0.0.1:* https://127.0.0.1:* http://0.0.0.0 https://0.0.0.0 http://0.0.0.0:* https://0.0.0.0:*] OLLAMA_RUNNERS_DIR: OLLAMA_TMPDIR:]"

[jmorganca]

This may be generally be an anti-pattern but could we use init() in this case? It might remove the need for the mutex since it the values will be initialized before the main function runs.

[dhiltgen]

I wanted a bit more control on when the vars were loaded so we could have unit test cases that do os.Setenv(...) then grab init or call other routines that need variables init'd. If we use init() then it would read the var before we updated it.

[dhiltgen]

Refactored to do both - primarily init() driven with an exposed function to reload if we want to fiddle with env vars at runtime and have them respected.

[jmorganca]

Thanks so much for doing this... some mostly cosmetic suggestions but this looks good

[jmorganca]

A few more naming suggestions but otherwise looks good