Managed HSMs are not purged

[heaths]

When running azd down --force --purge, Managed HSMs - a more secure, lifetime-billed Key Vault-like secure container - are not purged. These cost money even in deleted states and should be purged. Key Vaults, comparatively, are billed on a per-call basis so cost nothing when in a deleted state; though, if someone wants to reuse the same names, it can be a barrier.

[heaths]

Found while working on heaths/azcrypto#36. Managed HSMs were not being purged nor was there any prompt. These are highly secure but expensive resources and are still billed in a deleted state.