feat(llm): copilot (closes #68) (#116)

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

lua/avante/config.lua

@@ -9,7 +9,7 @@ M.defaults = {
   debug = false,
   ---Currently, default supported providers include "claude", "openai", "azure", "deepseek", "groq"
   ---For custom provider, see README.md
-  ---@alias Provider "openai" | "claude" | "azure" | "deepseek" | "groq" | string
+  ---@alias Provider "openai" | "claude" | "azure" | "deepseek" | "groq" | "copilot" | string
   provider = "claude",
   ---@type AvanteSupportedProvider
   openai = {
@@ -19,6 +19,16 @@ M.defaults = {
     max_tokens = 4096,
     ["local"] = false,
   },
+  ---@type AvanteCopilotProvider
+  copilot = {
+    endpoint = "https://api.githubcopilot.com",
+    model = "gpt-4o-2024-05-13",
+    proxy = nil, -- [protocol://]host[:port] Use this proxy
+    allow_insecure = false, -- Allow insecure server connections
+    timeout = 30000, -- Timeout in milliseconds
+    temperature = 0,
+    max_tokens = 8192,
+  },
   ---@type AvanteAzureProvider
   azure = {
     endpoint = "", -- example: "https://<your-resource-name>.openai.azure.com"