Support packaging and pushing a specified chart only

[superbrothers]

This PR supports packaging and pushing a specified chart only.

I want to release a specified chart with a specified chartVersion in a repository containing multiple charts. For example, the workflow would be as follows.

name: Release Charts

on:
  push:
    tags: ["**"]

jobs:
  release:
    runs-on: ubuntu-latest
    steps:
      - name: Get the chart name and version from the tag
        uses: actions/github-script@v6
        id: info
        with:
          script: |
            const tag = process.env.GITHUB_REF_NAME
            // The tag name is assumed to be `<chart name>-<chartVersion>`.
            const matches = tag.match(/^(.+)-([0-9]+\.[0-9]+\.[0-9]+)$/)
            console.log(matches)
            core.setOutput('name', matches[1])
            core.setOutput('version', matches[2])

      - name: Checkout
        uses: actions/checkout@v3

      - name: Publish Helm chart
        uses: stefanprodan/helm-gh-pages@master
        with:
          token: ${{ secrets.GITHUB_TOKEN }}
          chart_dir: charts/${{steps.info.outputs.name}}
          chart_version: ${{steps.info.outputs.version}}

[superbrothers]

@stefanprodan Please review this PR.

[ddfreiling]

This would be nice to have!