API key header default way

[Bercof]

Is your feature request related to a problem? Please describe.
The default way to set httpClient header is openai-style Authorization: Bearer ... now. But comparing to official python-openai library the default way is Azure-style api_key ... (here is source)
There is only one option to influence api key header: ProviderType.

Describe the solution you'd like
To avoid breaking changes my idea is to introduce new option AuthorizationHeaderType with explicit default value Undefined. At OpenAIService constructor AuthorizationHeaderType may be checked and may be set depending on ProviderType value.

Create enum:

public enum AuthorizationHeaderType
{
    Undefined = 0,
    AuthorizationHeader = 1,
    ApiKey = 2
}

Add new attribute to class OpenAiOptions:

public AuthorizationHeaderType AuthorizationHeaderType { get; set; } = AuthorizationHeaderType.Undefined;

Replace lines switch (settings.ProviderType) {...} at OpenAIService constructor:

if (settings.AuthorizationHeaderType == AuthorizationHeaderType.Undefined)
{
  switch (settings.ProviderType)
  case ProviderType.Azure:
      settings.AuthorizationHeaderType =  AuthorizationHeaderType.ApiKey;
      break;
  case ProviderType.OpenAi:
  default:
      settings.AuthorizationHeaderType =  AuthorizationHeaderType.AuthorizationHeader;
      break;

}

switch (settings.AuthorizationHeaderType)
{
  case AuthorizationHeaderType.ApiKey:
      _httpClient.DefaultRequestHeaders.Add("api-key", settings.ApiKey);
      break;
  case AuthorizationHeaderType.AuthorizationHeader:
  default:
      _httpClient.DefaultRequestHeaders.Add("Authorization", $"Bearer {settings.ApiKey}");
      break;
}

Describe alternatives you've considered
AuthorizationHeaderType attribute at OpenAiOptions may be nullable.