support DAP subagency parameter

[Aidan Feldman]

Background information

We have been asked to add a subagency=TTS parameter to all TTS sites. uswds-jekyll doesn't support this at the moment.

Acceptance criteria

• uswds-jekyll allows the subagency to be specified

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The assignee can add some checkboxes as a "sketch" of the steps to complete, which may evolve.

[Ryan Wold]

#205

And see 18F/agile#113 for an example of subagency being implemented.

Steps

If you're using the uswds-jekyll .gem,

1. add dap_subagency to your config.yml file.

[Aidan Feldman]

Released as part of 5.0.1.