Support Export & Import using Activation Tokens

[choufraise]

NATS supports cross-account exporting to either all or explicit accounts that have access to Activation Tokens. NAuth Account CRD does not support Activation Tokens today, hence all exports are all "public" and allows any other account to import from it.

The same applies to importing "private" streams, the Activation Token needs to be provided for the importing Account.

Add support for Activation Tokens in export/import.

References:

• NATS - JWT Security - Connecting Accounts
• NATS - nsc- Private Streams

[kejne]

It would be useful that there is a dedicated signing key for exports so that an export can be done to several accounts that all have restricted subjects - all using different signing keys that can be rotated individually.

The same goes for Users in order to have more fine grained control.

Looking at creating a separate SigningKey CRD which can be used to separate concerns.