Deny external access to non-personal accounts

[s8sato]

The stronger the trigger authority, the higher the risk of compromise of the corresponding private key. Such a system-side trigger authority should be a system-side account whose ID would be a pseudo public key that completely denies external access at authentication.

Addendum

With the resolution of #5441, data triggers now inherit the entrypoint authorities, eliminating that security risk. However, this issue still needs to be addressed for non-personal time trigger authorities, multisig accounts, and the genesis account.

[s8sato]

This also serves to prevent multisig monopoly: https://github.com/hyperledger/iroha/pull/5027#discussion_r1742295971

[s8sato]

Similar concepts:

• Ethereum's Contract Accounts
• Solana's Program Derived Addresses

[s8sato]

The genesis account will be replaced with a system account as well: https://github.com/hyperledger-iroha/iroha/pull/5488#discussion_r2226840113