Add issue template for better orientation

[SimonFrings]

This pull request adds issue templates to this project.

With GitHub Discussions now activated on an organizational level (as discussed in #460), it makes sense to add issue templates to each ReactPHP repository to show users where they have to open up specific tickets:

• New feature ideas and questions belong in ReactPHP discussions. GitHub discussions are more long-lived than issues, thus enabling better visibility for users.
• We'll continue to use issues for bug reports. These bugs will be fixed at some point and then belong in closed issues. Additionally I won't add a bug template to reactphp/reactphp. IMO it makes no sense to report a bug in this repository. All bugs should be reported inside the related repo (http, socket, dns, etc.).
• Security issues should be reported to us via email. It is important not to make security-related issues public before they have been fixed!

I will file pull requests to add issue templates for each ReactPHP repository. Repos like https://github.com/reactphp/branding or https://github.com/reactphp/.github won't receive them (makes no sense).

[nhedger]

I believe it's possible to create default issue templates at the organization level.

• https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/creating-a-default-community-health-file

This should save you from having to open PR on all repositories.

[SimonFrings]

@nhedger You're totally right, the only thing I'd have to do is to add the ISSUE_TEMPLATE folder to the .github folder inside reactphp/.github and it's done.

The downside is that EVERY project inside the ReactPHP organisation gets the same issue template. This may make sense for most projects (like dns, http, etc.) but not for something like reactphp/branding or reactphp/reactphp. I would instantly do this if GitHub had some kind of functionality to exclude specific repositories, but I didn't find anything similar.

In conclusion: I am willing to take the slightly longer road and do it for every repository individually (which means only to copy-paste at some point 😄). Just feels right ^^

[SimonFrings]

@clue, @WyriHaximus I had to rebase my chnages to match #462, now all tests are green and this is ready for review.

[WyriHaximus]

👍

[clue]

@SimonFrings Thank you for the update, changes LGTM!