Add `flow accounts list` command to validate accounts from flow.json

[chasefleming]

Description:

We should add a new CLI command:

flow accounts list

Purpose

This command will:

• List all accounts defined in the local flow.json.

• For each account, display:

  • Name (alias from flow.json)
  • Address (configured address)
  • Networks (testnet, mainnet, etc. where the account is defined)
  • Status: whether the account is valid/exists on each specified network.