zed_extension_api: Fork new version of extension API (#30611)

This PR forks a new version of the `zed_extension_api` in preparation
for new changes.

Release Notes:

- N/A

crates/extension_api/wit/since_v0.6.0/context-server.wit

@@ -0,0 +1,11 @@
+interface context-server {
+    /// Configuration for context server setup and installation.
+    record context-server-configuration {
+        /// Installation instructions in Markdown format.
+        installation-instructions: string,
+        /// JSON schema for settings validation.
+        settings-schema: string,
+        /// Default settings template.
+        default-settings: string,
+    }
+}