feat[ANV]: add flag to allow brew package upgrade

When theres a new package anvil wont install, whereas brew will.

Add a switch say `--override` which allows to upgrade.

```
anvil install forklift --concurrent

=== Installing 'forklift' ===
💙 forklift is already available on the system
```
```
❯ brew install forklift
==> Upgrading 1 outdated package:
forklift 4.4.1 -> 4.4.2
==> Upgrading forklift
```