text: Title: SimpleJWT integration doesn't take into account the settings AUTH_HEADER_NAME
  Body: Hi, just figuring this out today because I had to use a custom header for simplejwt auth
  
  
  **Describe the bug**
  SimpleJwt can be configured by using a dict in the settings.py of a django project.
  `SIMPLE_JWT = {
      'AUTH_HEADER_NAME' : "HTTP_X_TOKEN" # translate to X-token as header.
  }`
  But the current implementation doesn't take this settings into account : 
  
  `class SimpleJWTScheme(OpenApiAuthenticationExtension):
      target_class = 'rest_framework_simplejwt.authentication.JWTAuthentication'
      name = 'jwtAuth'
  
      def get_security_definition(self, auto_schema):
          from rest_framework_simplejwt.settings import api_settings
  
          if len(api_settings.AUTH_HEADER_TYPES) > 1:
              warn(
                  f'OpenAPI3 can only have one "bearerFormat". JWT Settings specify '
                  f'{api_settings.AUTH_HEADER_TYPES}. Using the first one.'
              )
          return {
              'type': 'http',
              'scheme': 'bearer',
              'bearerFormat': api_settings.AUTH_HEADER_TYPES[0],
          }`
  
  Where the return  should become something I guess like 
  `{'type':'apiKey', 'in': 'header', 'name': api_settings.SIMPLE_JWT['AUTH_HEADER_NAME']}`
  
  
  **To Reproduce**
  
  Change simplejwt header setting.
  
  **Expected behavior**
  
  Authentication should scheme should follow simplejwt settings.
  
  I may have time to make a PR if needed.
  