Scaffold: set arbitrary headers

[BrianHenryIE]

Feature Request

• [x] Yes, I reviewed the contribution guidelines.

Describe your use case and the problem you are facing

I'm using wp scaffold plugin for the first time and the very next thing I want to do after it completes is to set the value of the Update URI header.

Describe the solution you'd like

Something similar to wp config set, ~ wp scaffold plugin set "Update URI" https://example.com

I could see this being used in CI for the Version, Tested up to, Requires PHP, WC requires at least, and WC tested up to fields.

So maybe scaffold isn't the correct term.

I'm pretty sure there's code in WP CLI that tokenizes PHP but I can't remember where I saw it. Probably in the doc-block parsing. I presume the same approach would be used here.

[swissspidy]

Slightly related: #17

Maybe wp theme|plugin header set|get

There's some docbloc parsing for these file headers in core & i18n-command, but none for writing them.