chore: track usage of built-in example templates (#15671)

Addresses https://github.com/coder/nexus/issues/99.

Changes:
- Save the id of the built-in example template used to create a template
version in the database
- Include the example id in telemetry

coderd/database/dump.sql

@@ -1217,7 +1217,8 @@ CREATE TABLE template_versions (
     created_by uuid NOT NULL,
     external_auth_providers jsonb DEFAULT '[]'::jsonb NOT NULL,
     message character varying(1048576) DEFAULT ''::character varying NOT NULL,
-    archived boolean DEFAULT false NOT NULL
+    archived boolean DEFAULT false NOT NULL,
+    source_example_id text
 );
 
 COMMENT ON COLUMN template_versions.external_auth_providers IS 'IDs of External auth providers for a specific template version';
@@ -1245,6 +1246,7 @@ CREATE VIEW template_version_with_user AS
     template_versions.external_auth_providers,
     template_versions.message,
     template_versions.archived,
+    template_versions.source_example_id,
     COALESCE(visible_users.avatar_url, ''::text) AS created_by_avatar_url,
     COALESCE(visible_users.username, ''::text) AS created_by_username
    FROM (template_versions