[feat] Add basic support for IBM's watsonx code assistant (#2617)

Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>

lua/avante/config.lua

@@ -26,7 +26,7 @@ M._defaults = {
   ---@alias avante.Mode "agentic" | "legacy"
   ---@type avante.Mode
   mode = "agentic",
-  ---@alias avante.ProviderName "claude" | "openai" | "azure" | "gemini" | "vertex" | "cohere" | "copilot" | "bedrock" | "ollama" | string
+  ---@alias avante.ProviderName "claude" | "openai" | "azure" | "gemini" | "vertex" | "cohere" | "copilot" | "bedrock" | "ollama" | "watsonx_code_assistant" | string
   ---@type avante.ProviderName
   provider = "claude",
   -- WARNING: Since auto-suggestions are a high-frequency operation and therefore expensive,
@@ -348,6 +348,16 @@ M._defaults = {
         },
       },
     },
+    ---@type AvanteSupportedProvider
+    watsonx_code_assistant = {
+      endpoint = "https://api.dataplatform.cloud.ibm.com/v2/wca/core/chat/text/generation",
+      model = "granite-8b-code-instruct",
+      timeout = 30000, -- Timeout in milliseconds
+      extra_request_body = {
+        -- Additional watsonx-specific parameters can be added here
+      },
+    },
+
     ---@type AvanteSupportedProvider
     vertex_claude = {
       endpoint = "https://LOCATION-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/publishers/antrhopic/models",