Templating project build beyond plugin-versions

Blowdryer `1.7.0` added a [plugin-versions](https://github.com/diffplug/blowdryer#plugin-versions) feature which has removed a lot of headache from maintaining our fleet of builds.

It would be nice to have similar templating available for e.g GitHub Actions files, maybe `.gitattributes`, stuff like that. No imminent plans to implement this, but open to PRs.

I lean towards an API along these lines:

```gradle
// blowdryer-scripts
actions.template <- file whose content is a newline delimited list of paths to copy from scripts into the repository
.github/workflows/gradle-wrapper-validation.yml
.github/workflows/ci.yml

// settings.gradle
blowdryerSetup {
applyTemplate 'actions.template', {
omitFile '.github/workflows/ci.yml'
modifyFile '.github/workflows/gradle-wrapper-validation.yml', {
replace '8', '11'
}
}
}
```