FR: add rule template/object-shorthand

[rafaelss95]

Angular v12.1.0 brought us the support for shorthand property declarations in templates and so we can write <div [test]="{ a, b, c }"></div> instead of <div [test]="{ a: a, b: b, c: c }"></div>.

In order to help to maintain a consistent codebase, I'd like to propose a rule with the same ideia of object-shorthand, with a single option that indicates that we should always (default) or never use shorthand form.

Examples:

{
  "rules": {
    "@angular-eslint/template/object-shorthand": ["error", "always"]
  }
}

<div [test]="{ a: a, b: b, c: c }"></div> ❌ => `a`, `b` and `c` should be shorthand
<div [test]="{ a, b: 1, c: anotherName }"></div> ✅

{
  "rules": {
    "@angular-eslint/template/object-shorthand": ["error", "never"]
  }
}

<div [test]="{ a, b: 1, c: anotherName }"></div> ❌ => `a` should not be shorthand
<div [test]="{ a: a, b: b, c: c }"></div> ✅