Support regular expression in RBAC role node_labels matchers

[klizhentas]

** Description

Add support for regular expression in label keys and values

Support following formats: scalar values with regexp:

allow:
  node_labels:
    'env: '^production|staging$'
deny:
  node_labels:
    'env: '^test$'

list values:

allow:
  node_labels:
    'env: ['^production|staging$', 'test']
deny:
  node_labels:
    'env: ['^test$', 'list']

[russjones]

Fixed in #2262.

[russjones]

Reopening to make documentation ticket.