Add tags entry in molecule yaml schema

[gciavarrini]

Feature description

It would be useful to have the possibility to add tags section (i.e., list of strings) to molecule.yml file.
The tags section can be optional.

This new feature will enable a behavior similar to the Ansible one.

Expected behavior

Expected molecule.yml can be:

---
platforms:
  - name: name1
        location: westeurope
        resourcegroup_name: groupA
        …. etc …
scenario:
  test_sequence:
       - create
       - verify
       - destroy
  destroy_sequence:
    - destroy

provisioner:
  name: ansible
  playbooks:
        create: create.yml
        verify: verify.yml
        destroy: destroy.yml
verifier:
  name: ansible

tags:
    - regression
    - new_feature

Usage scenarios

Possible usage scenarios are:

• As ways to select molecule testing scenarios.
  E.g. test all molecule scenarios with regression tag every time there is a new PR in CI.
• As tags for infra created if created on hyperscalers that support tagging.