feat: allow overriding provider headers (#2161)

lua/avante/providers/openai.lua

@@ -497,12 +497,6 @@ function M:parse_curl_args(prompt_opts)
     ["Content-Type"] = "application/json",
   }
 
-  if provider_conf.extra_headers then
-    for key, value in pairs(provider_conf.extra_headers) do
-      headers[key] = value
-    end
-  end
-
   if Providers.env.require_api_key(provider_conf) then
     local api_key = self.parse_api_key()
     if api_key == nil then
@@ -536,7 +530,7 @@ function M:parse_curl_args(prompt_opts)
     url = Utils.url_join(provider_conf.endpoint, "/chat/completions"),
     proxy = provider_conf.proxy,
     insecure = provider_conf.allow_insecure,
-    headers = headers,
+    headers = Utils.tbl_override(headers, self.extra_headers),
     body = vim.tbl_deep_extend("force", {
       model = provider_conf.model,
       messages = self:parse_messages(prompt_opts),