wip: adding azureopenai provider

[freemanpolys]

Hello,
I'm working on Azure OpenAI provider .
As Azure OpenAI is just another OpenAI implementation, I've just use composition to make it work.
As you can see, I currently use env variables to get Azure OpenAI Endpoint and Azure OpenAI ApiVersion.
Like ExtraHeaders, I propose to add ExtraConfs to Config struct to handle every provider additional configs. What do you think ?

type Config struct {
 ....
ExtraConfs          map[string]string
}``