Validate collection metadata

[chouseknecht]

Adds validation for collection metadata. Collection metadata currently expects 6 values, for example:

name: foo.foo
authors:
  - chouseknecht
description: a whole bunch of foo for you
license: GPL-3.0-or-later
version: 0.0.1
keywords:
  - foo
  - bar
  - baz

Validation rules check:

• name, description, version and license are required
• version matches semantic version format
• license is an SPDX license ID
• warns if license is deprecated
• keywords and authors are of type list
• keywords contain alphanumeric chars only

Lines up galaxy.yml expectations/validation with https://github.com/ansible/galaxy/pull/1173