Add brew cleanup --scrub flag variation

[garritfra]

Verification

• This issue's title and/or description do not reference a single formula e.g. brew install wget. If they do, open an issue at https://github.com/Homebrew/homebrew-core/issues/new/choose instead.

Provide a detailed description of the proposed feature

Currently, brew cleanup -s triggers a cleanup with the scrub flag enabled. I would like to introduce a longer alias of this flag, --scrub, for usage in shell-scripts and alike.

What is the motivation for the feature?

Unlike the other flags on this command (e.g. -n == --dry-run), there is no long form for the scrub flag. When I first encountered this flag, I had to look up what the -s meant, which is arguably undesirable in terms of readability in longer shell-scripts. A --scrub variant would have made this a bit clearer.

How will the feature be relevant to at least 90% of Homebrew users?

It makes the CLI more consistent and comprehensible.

What alternatives to the feature have been considered?