cmd/config: Add core cask tap to output

[apainintheneck]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

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This information is occasionally useful when debugging so we should include it by default to make our lives easier.

$ brew config
HOMEBREW_VERSION: 4.2.0-50-g536b37c
ORIGIN: https://github.com/Homebrew/brew
HEAD: 536b37c7665763d30819919a532996d593ef0aa0
Last commit: 4 minutes ago
Core tap origin: https://github.com/Homebrew/homebrew-core
Core tap HEAD: 58c547f2a50e995baf7279f47c1190cab8bcb1f2
Core tap last commit: 6 hours ago
Core tap branch: master
Core tap JSON: 22 Dec 05:08 UTC
Core cask tap origin: https://github.com/Homebrew/homebrew-cask
Core cask tap HEAD: 3c6b6215ed536a26d2cbe18b2e03de0f2ed3c0af
Core cask tap last commit: 3 hours ago
Core cask tap branch: master
Core cask tap JSON: 22 Dec 05:08 UTC
HOMEBREW_PREFIX: /usr/local
HOMEBREW_AUTOREMOVE: set
HOMEBREW_CASK_OPTS: []
HOMEBREW_DEVELOPER: set
HOMEBREW_DISPLAY: /private/tmp/com.apple.launchd.4yAKvlGURn/org.macosforge.xquartz:0
HOMEBREW_EDITOR: code
HOMEBREW_MAKE_JOBS: 4
HOMEBREW_SORBET_RUNTIME: set
Homebrew Ruby: 3.1.4 => /usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/3.1.4/bin/ruby
CPU: quad-core 64-bit ivybridge
Clang: 12.0.0 build 1200
Git: 2.24.3 => /Applications/Xcode.app/Contents/Developer/usr/bin/git
Curl: 7.64.1 => /usr/bin/curl
macOS: 10.15.7-x86_64
CLT: 12.0.0.32.29
Xcode: 12.4

[MikeMcQuaid]

Looks good! What might be nice for a follow-up is slimming this down a bit. For a bunch of other brew config things e.g. environment variables we only show non-default values so could perhaps hide the default origins if they are what we expect, hide master branches, etc.