feat(devbox): add provisioning_tier to LaunchParameters (alpha)

Adds the optional provisioning_tier field ('standard' | 'flex') to the shared
LaunchParameters interface (used by both DevboxCreateParams and DevboxView),
matching the field now exposed in the OpenAPI spec.

Hand-applied ahead of the next Stainless regeneration so the alpha customer
can use the field immediately. provisioning_tier is intentionally kept out of
the public docs (stripped from the documented spec upstream).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: claude

src/resources/shared.ts

@@ -284,6 +284,12 @@ export interface LaunchParameters {
    */
   network_policy_id?: string | null;
 
+  /**
+   * (Optional) standard is default and flex is lazily provisioned and may be
+   * pre-empted.
+   */
+  provisioning_tier?: 'standard' | 'flex' | null;
+
   /**
    * A list of ContainerizedService names to be started when a Devbox is created. A
    * valid ContainerizedService must be specified in Blueprint to be started.