Support key export from Key Vault

[heaths]

For Key Vault 7.2-preview, we need to add support to export keys. This would be a method like KeyClient.ExportKey that takes the key name, key version (both required), and a body with the KeyExportParameters model found in the link below. This only has a single required property named environment (model property: env), so we should take this as a parameter. This returns a KeyVaultKey (model KeyBundle).

This requires a number of other changes:

• Add optional Exportable boolean property to KeyProperties.
• Add ReleasePolicy property to KeyProperties of type KeyReleasePolicy.
• Add PublicExponent integer property to CreateKeyOptions.
• Add "export" to KeyOperation enum. This will correctly impact the CreateKeyOptions class and the KeyClient.UpdateKey method..
• Add ReleasePolicy property to CreateKeyOptions.
• Add ReleasePolicy property to ImportKeyOptions.

See the service version 7.1 -> 7.2-preview diff 🔒 for details.

[sadasant]

Note from Heath, from the teams chat:

[1:10 PM] Heath Stewart
Service - KeyVault - hold off on implementing secure key release for now. The design is being changed after last week's service/client sync-up.

[heaths]

[9/16 2:54 PM] Heath Stewart
For now, hold off. I looped you all into a thread where MHSM just wants this as an opaque JSON blob, so model structure won't matter.

😉

[sadasant]

I didn't see that on time! Thank you!

[sadasant]

I'll push this for next month's release due to time budget.

[sadasant]

Maor is currently assigned to the update and cleanup of the Key Vault Admin API. We won't be releasing export/release this month though, so we will likely push this issue for a later date, but in the mean time I'll keep this issue open so Maor can decide.

[heaths]

This should be moved out of February GA and done for 7.3-preview service version.

[maorleger]

I created #16086 to support SKR. Key Export is not yet ready on the service side. Moving this to backlog

[maorleger]

This doesn't need to be tracked, let's add a new task when key export is ready on the service side.