feat(llm): add support for parsing secret vault (#200)

Signed-off-by: Aaron Pham <contact@aarnphm.xyz>

lua/avante/providers/openai.lua

@@ -26,10 +26,6 @@ local M = {}
 
 M.api_key_name = "OPENAI_API_KEY"
 
-M.has = function()
-  return os.getenv(M.api_key_name) and true or false
-end
-
 M.parse_message = function(opts)
   local user_prompt = opts.base_prompt
     .. "\n\nCODE:\n"
@@ -91,7 +87,7 @@ M.parse_curl_args = function(provider, code_opts)
     ["Content-Type"] = "application/json",
   }
   if not P.env.is_local("openai") then
-    headers["Authorization"] = "Bearer " .. os.getenv(base.api_key_name or M.api_key_name)
+    headers["Authorization"] = "Bearer " .. provider.parse_api_key()
   end
 
   return {