Support `--recursive` flag

[Mitch Harvey]

Hey, I have come across a problem when passing the recursive flag into the action. I get the following error

  Failed to find workspaces; cannot use --recursive and --chdir at the same time

which makes sense as this line will always pass the chdir argument into the command. I am wondering if it is possible to add a flag to not send this if the user is specifying the recursive flag. I am thinking of possibly not setting tflint_target_dir to the default (as it shouldn't need to be passing in a . value anyway as it just indicates no changing of the directory) and only providing the command if there is a value provided.

I am happy to do the PR to get this change out, I am just seeking guidance on which way to approach this.

A sample of how we run this command is

      - name: Terraform Lint
        id: tflint
        uses: reviewdog/action-tflint@master
        with:
          github_token: ${{ secrets.github_token }}
          flags: "--enable-rule=terraform_unused_declarations --disable-rule=terraform_typed_variables --recursive"
          filter_mode: nofilter
          tflint_rulesets: "aws"
          level: "error