Prohibit known public keys from being used in some environments

### Problem

The hedera-local-node generates a handful of accounts with well known public/private keys that are to be used for documentation / local testing purposes. An unsophisticated user/developer *may* use these well known keys to create accounts on mainnet, leaving themselves vulnerable to theft by anybody who discovers them.

### Solution

We should have a flag in the system to restrict well known keys from being used, and enable that flag at least on mainnet, and probably also on testnet, and maybe even on previewnet. These well known keys are those used by Ethereum devs and those used in hedera-local-node.

### Alternatives

_No response_

The issue names no files, tests, or entry points. Start by locating the configuration or validation path for public keys and reviewing the known keys from hedera-local-node and Ethereum development use; done means a flag prevents those keys in the selected environments, including mainnet and possibly testnet or previewnet.

Written by the indexing model from the issue text.