Close #865

This pull request adds an input github_token_for_tflint_init, which is a GitHub Access Token for tflint --init.
If this is set, the value is passed to tflint --init as the environment variable GITHUB_TOKEN.
Otherwise, the input github_token is used instead.

This input is useful for GitHub Enterprise Servers.
You can post comments and reviews to a GitHub Enterprise Server with github-comment and reviewdog, and download tflint plugins from github.com.

- uses: suzuki-shunsuke/github-action-tflint@v0.1.1
  with:
    github_token: ${{ secrets.GITHUB_TOKEN }} # GitHub Access token of GitHub Enterprise Server
    github_token_for_tflint_init: ${{ secrets.GH_TOKEN_FOR_TFLINT_INIT }} # GitHub Access token of github.com
    github_comment: true