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

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

For example:
```YAML
$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
````