Add machine locking to Pro plan features

Closes STA-4864

Author: laurakalbag

docs/studio-pro-plan.mdx

@@ -13,6 +13,7 @@ title: Stately Studio Pro plan
 - [Version history](/versions.mdx)
 - [Import from GitHub](/import-from-github.mdx)
 - [Live simulation mode](/live-simulation.mdx)
+- [Lock machines](/lock-machines.mdx)
 - [Color states and transitions](/colors.mdx)
 - [Priority support](/studio-pro-plan.mdx#priority-support)
 - GitHub Sync (coming soon!)

versioned_docs/version-5/studio-pro-plan.mdx

@@ -13,6 +13,7 @@ title: Stately Studio Pro plan
 - [Version history](/versions.mdx)
 - [Import from GitHub](/import-from-github.mdx)
 - [Live simulation mode](/live-simulation.mdx)
+- [Lock machines](/lock-machines.mdx)
 - [Color states and transitions](/colors.mdx)
 - [Priority support](/studio-pro-plan.mdx#priority-support)
 - GitHub Sync (coming soon!)