Disable account creation command for mainnet

[chasefleming]

Issue Description:

Currently, the flow accounts create command is enabled for mainnet in the CLI. This command allows users to create accounts directly on the mainnet, which could lead to unintended consequences or misuse. To prevent this, the flow accounts create command should be disabled specifically for the mainnet.

Suggested Solution:

When users attempt to use flow accounts create on mainnet, it should display a message guiding them on how to create an account for mainnet using alternative methods.

[turbolent]

What are the alternate methods?

[sisyphusSmiling]

bumping this due to recent question in discord - Do we have alternative dev-focussed paths for Mainnet account creation?