Plugin to maintain .mergify.yml

As a possible alternative to #39, would there be any interest in something like the following rough draft? Basically it keeps the jobs in .mergify.yml up to date when running githubWorkflowGenerate:

import java.io.{File, FileInputStream}
import java.{util => ju}

import scala.collection.JavaConverters._
import scala.util.matching.Regex

import org.yaml.snakeyaml.Yaml
import sbt.AutoPlugin
import sbt.io.IO
import sbtghactions.GenerativeKeys.{githubWorkflowGenerate, githubWorkflowGeneratedCI}
import sbtghactions.GenerativePlugin


object Mergify extends AutoPlugin {
  override def requires = GenerativePlugin
  override def trigger = allRequirements

  type Dict = ju.Map[String, AnyRef]

  override def projectSettings = Seq(
    githubWorkflowGenerate := {
      githubWorkflowGenerate.value
      githubWorkflowGeneratedCI.value
        .find(_.id == "build")
        .foreach { job =>
          val yaml = new Yaml
          val res = yaml.load[Dict](new FileInputStream(".mergify.yml"))
          val conditions =
            res
              .get("pull_request_rules").asInstanceOf[ju.List[Dict]].asScala.map(_.asScala)
              .find(_ ("name") == "Automatically merge successful scala-steward PRs").get
              .apply("conditions").asInstanceOf[ju.List[String]].asScala

          val existing = conditions.filter(_.matches(s"status-success=${Regex.quote(job.name)} \\(.*\\)"))
          conditions --= existing

          val concreteJobNames = for (o <- job.oses; s <- job.scalas; v <- job.javas) yield s"${job.name} ($o, $s, $v)"

          conditions ++= concreteJobNames.map(name => s"status-success=$name")

          IO.write(new File(".mergify.yml"), yaml.dumpAsMap(res))
        }
    }
  )
}

Start by reading the proposed AutoPlugin and the githubWorkflowGenerate/githubWorkflowGeneratedCI entry points in the issue, then inspect how .mergify.yml is structured. The issue identifies no repository files or tests, so the intended scope and validation approach need to be established first. Done would mean an agreed plugin design that updates the relevant Mergify status-success jobs when workflow generation runs.