Add support for bulk-creating/editing issue label and type metadata

[briandominick]

Design a YAML format for defining and pushing multiple label and type entries to a given repo/project's issues system.

For example:

$meta:
  tags:
    delimiter: ":" # separator between key and value of parameterized labels
tags:
  - name: priority
    reqd: 1
    values:
      - name: stretch # priority:stretch
        desc: This would be nice to have, but it's not essential for the assigned release.
        color: '#00FF00'
      - name: critical # priority:critical
        desc: This issue MUST make it into the assigned release.
        color: '#FF0000'
  - name: good first issue
    desc: Appropriate for new contributors.
    color: blue
  - name: component
    reqd: 1..
    color: purple
    values:
      - api # component:api
      - webui # component:webui
      - database # component:database
      - infrastructure # component:infrastructure