Update pathogen-repo-ci to "generic"/"smart" workflow

[genehack]

Context

Per recent discussion, as well as various legacy conversations here, here, and here, we want to update the pathogen-repo-ci GitHub Action to a "strict" version that can be used across all of our "modern" pathogen repos with zero configuration on the consuming repo side.

Description

Update the pathogen-repo-ci workflow so that:

1. For each build-name (i.e., each of ingest, phylogenetic, and nextclade):
   a. If the repo contains a <build-name>/Snakefile file and a <build-name>/build-configs/ci/config.yaml file
   b. Run nextstrain build <build-name> --configfile build-configs/ci/config.yaml

The consuming repo will be responsible for providing an appropriate config file that either sets up appropriate example data or results in a subset of a full workflow being run, so as to validate that the repo workflows have not been broken by a change.

Examples

This workflow, plus the appropriate build-config files, should be sufficient to enable CI for a pathogen repo:

name: CI
on:
  - push
jobs:
  ci:
    name: CI
    uses: nextstrain/.github/workflows/pathogen-repo-ci.yaml

[genehack]

This was opened in the wrong repo, and is being closed in favor of nextstrain/.github#89, which has the supreme advantage of being in the correct repo.

Those responsible for the error have been sacked.