Add `--fund` flag to forc-node to pre-fund accounts

## Description
To fund accounts, one must manually edit the `chainspec` with funded accounts.
This is a hassle as it requires understanding the `chainspec`, editting and persisting the file, then referencing the file in the `forc-node` command.
^ Also this doesn't work reliably (to be validated).

## Proposed Solution
Add a `--fund` flag to forc-node that allows direct account funding:
```sh
forc node local --fund :,:
```
or to also support `amount`
```sh
forc node local --fund ::,::
```

With an optional `--fund-amount` flag to override the default funding amount.

## Benefits
- Simplifies testing with wallets/accounts
- Eliminates need to manually edit chainspecs