feat: structured output with alr --format show

[mosteo]

Show accepts now --format:

$ alr --format show hello
{
  "authors": [
    "Alejandro R. Mosteo"
  ],
  "depends-on": [
    {
      "libhello": "^1.0"
    }
  ],
  "description": "'Hello, world!' demonstration project",
  "executables": [
    "hello"
  ],
  "licenses": "MIT",
  "maintainers": [
    "Alejandro R. Mosteo <alejandro@mosteo.com>"
  ],
  "maintainers-logins": [
    "mosteo"
  ],
  "name": "hello",
  "origin": {
    "commit": "5715870bf1637ac06c87a3db580d4efdfd5daeed",
    "url": "git+https://github.com/alire-project/hello.git"
  },
  "tags": [
    "hello",
    "demo"
  ],
  "version": "1.0.2",
  "website": "https://github.com/alire-project/hello"
}

Also did a general review of all the commands to forbid --format when not applicable.

User changes didn't mention --format when it was introduced, so added that too.

Fixes #1151
Fixes #1600

PR creation checklist

• A test is included, if required by the changes.
• doc/user-changes.md has been updated, if there are user-visible changes.