feat: add custom AI provider icons and instance-based model picker grouping (#27026)

coderd/database/dump.sql

@@ -1495,6 +1495,7 @@ CREATE TABLE ai_providers (
     settings_key_id text,
     created_at timestamp with time zone DEFAULT now() NOT NULL,
     updated_at timestamp with time zone DEFAULT now() NOT NULL,
+    icon text DEFAULT ''::text NOT NULL,
     CONSTRAINT ai_providers_name_check CHECK ((name ~ '^[a-z0-9]+(-[a-z0-9]+)*$'::text))
 );