[Core feature request] Add support to Workflow Dispatch Inputs

Start with GitHub's workflow_dispatch inputs syntax and the existing WorkflowDispatch/Input usage shown in the issue. Trace how workflow triggers and environment expressions are modeled, then compare generated output with the linked kotest example. Done means callers can declare and reference dispatch inputs without the event.inputs workaround.

Discussed in Kotlin's Slack: https://app.slack.com/client/T09229ZC6/C02UUATR7RC/thread/C02UUATR7RC-1682902161.628869

What feature do you need?
Workflows Dispatch Inputs:
https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#onworkflow_dispatchinputs

Do you have an example usage?

https://github.com/kotest/kotest/blob/80bc809be1e0452dc1f3ee2e67aec2f6c7f6c251/.github/workflows/release_base.yml#L15

env:
   RELEASE_VERSION: ${{ inputs.version }}
   OSSRH_USERNAME: ${{ secrets.OSSRH_USERNAME }}
   OSSRH_PASSWORD: ${{ secrets.OSSRH_PASSWORD }}
   ORG_GRADLE_PROJECT_signingKey: ${{ secrets.SIGNING_KEY }}
   ORG_GRADLE_PROJECT_signingPassword: ${{ secrets.SIGNING_PASSWORD }}
   GRADLE_OPTS: -Dorg.gradle.configureondemand=true -Dorg.gradle.parallel=false -Dkotlin.incremental=false -Dorg.gradle.jvmargs="-Xmx3g -XX:MaxMetaspaceSize=756m -XX:MaxPermSize=2048m -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8"

Is there a workaround for not having this feature? If yes, please describe it.

Yes. One can use WorkflowDispatch normally, and use expr { github["event.inputs.XXXX"]!! } to get the value when they need it.

workflow(
  name = "Publish",
  on = listOf(
    WorkflowDispatch(
      mapOf("RELEASE_VERSION" to Input("The release version", true, String))
    )
  ),
  sourceFile = __FILE__.toPath(),
  env = linkedMapOf(
    "OSSRH_USERNAME" to expr { OSSRH_USERNAME },
    "OSSRH_PASSWORD" to expr { OSSRH_PASSWORD },
    "ORG_GRADLE_PROJECT_signingKey" to expr { ORG_GRADLE_PROJECT_signingKey },
    "ORG_GRADLE_PROJECT_signingPassword" to expr { ORG_GRADLE_PROJECT_signingPassword },
    "RELEASE_VERSION" to expr { github["event.inputs.version"]!! }
  )
)