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/migrations/000277_template_version_example_ids.down.sql

@@ -0,0 +1,28 @@
+-- We cannot alter the column type while a view depends on it, so we drop it and recreate it.
+DROP VIEW template_version_with_user;
+
+ALTER TABLE
+    template_versions
+DROP COLUMN source_example_id;
+
+-- Recreate `template_version_with_user` as described in dump.sql
+CREATE VIEW template_version_with_user AS
+SELECT
+  template_versions.id,
+  template_versions.template_id,
+  template_versions.organization_id,
+  template_versions.created_at,
+  template_versions.updated_at,
+  template_versions.name,
+  template_versions.readme,
+  template_versions.job_id,
+  template_versions.created_by,
+  template_versions.external_auth_providers,
+  template_versions.message,
+  template_versions.archived,
+  COALESCE(visible_users.avatar_url, ''::text) AS created_by_avatar_url,
+  COALESCE(visible_users.username, ''::text) AS created_by_username
+FROM (template_versions
+  LEFT JOIN visible_users ON (template_versions.created_by = visible_users.id));
+
+COMMENT ON VIEW template_version_with_user IS 'Joins in the username + avatar url of the created by user.';

coderd/database/migrations/000277_template_version_example_ids.up.sql

@@ -0,0 +1,30 @@
+-- We cannot alter the column type while a view depends on it, so we drop it and recreate it.
+DROP VIEW template_version_with_user;
+
+ALTER TABLE
+    template_versions
+ADD
+    COLUMN source_example_id TEXT;
+
+-- Recreate `template_version_with_user` as described in dump.sql
+CREATE VIEW template_version_with_user AS
+SELECT
+  template_versions.id,
+  template_versions.template_id,
+  template_versions.organization_id,
+  template_versions.created_at,
+  template_versions.updated_at,
+  template_versions.name,
+  template_versions.readme,
+  template_versions.job_id,
+  template_versions.created_by,
+  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
+  LEFT JOIN visible_users ON (template_versions.created_by = visible_users.id));
+
+COMMENT ON VIEW template_version_with_user IS 'Joins in the username + avatar url of the created by user.';