feat: Update Terraform provider to support "dir" in "coder_agent" (#1219)

This allows users to specify a starting directory for shell sessions.

coderd/database/dump.sql

@@ -247,7 +247,8 @@ CREATE TABLE workspace_agents (
     operating_system character varying(64) NOT NULL,
     startup_script character varying(65534),
     instance_metadata jsonb,
-    resource_metadata jsonb
+    resource_metadata jsonb,
+    directory character varying(4096) DEFAULT ''::character varying NOT NULL
 );
 
 CREATE TABLE workspace_builds (