OpenAI API keys should be addressed with templates

[0xThresh]

Currently, the only way to set OPENAI_API_KEY or OPENAI_API_KEYS variables is through the extraEnvVars value on the chart. While this works, it would be better to have dedicated values for those environement variables, similar to what's in place for the OPENAI_API_BASE_URL and OPENAI_API_BASE_URLS variables.

Without setting these in the templates, a handful of issues can occur:

1. There is no obvious way to match up API key/ API endpoint pairs. Instead, you have to match up the API URL and key as the same index in their respective lists.
2. While the URL variables will set the value, users will have issues making use of those endpoints until keys are set manually through extraEnvVars or in the Admin Settings after starting Open WebUI.