Convert bug report issue template to form

[bendrucker]

This PR converts TFLint's bug report issue template into an issue form. I also plan to convert the feature template in a later PR.

I've been noticing a lot of low-effort bug reports that skip over critical details that would be needed to diagnose and solve the issue. Most often, this missing information is Terraform configuration in a large/complex module that the submitter doesn't want to hassle with isolating. Understandable, but an incomplete bug report does no one any good.

In addition to structuring the existing template as a form, I've made the following additions/changes:

• Users are encouraged to report ruleset-specific issues in their corresponding repository.
• The summary is expected to be plain, concise text, whereas the Introduction section of the template called for an HCL code block, without explanation of what that content should be.
• Users are required to specify the Command they used. While required, the value tflint is populated by default.
• Users are required to specify the Terraform Configuration. In the very rare case that the issue is not related to the root module (e.g., plugin downloading), users can enter a placeholder value. I'll either add a note about this to the description or consider making another form specifically for plugin issues.
• Users are required to specify the TFLint Configuration.
• Users are required to specify the Output.
• Users are required to specify the TFLint Version. For now, this is a simple input.
• Users are allowed to specify the Terraform Version, but are only encouraged to do so for cases where Terraform can parse the config but TFLint cannot.
• Users are asked to specify the operating systems where they've reproduced the problem. Previously this would have come from terraform -v which prints $GOOS_$GOARCH as part of its output. We could add this to tflint -v and go back to a textarea for that and remove this field entirely. I also internally debated whether this should be a dropdown or checkboxes. It's common to use macOS locally and Linux on the server so I went with checkboxes.

Syntax for issue forms:

https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/syntax-for-githubs-form-schema#input

[wata727]

Nice 👍