Update issue template

[stefanobaghino-da]

Mention the community forum instead of StackOverflow

changelog_begin
changelog_end

Pull Request Checklist

• Read and understand the contribution guidelines
• Include appropriate tests
• Set a descriptive title and thorough description
• Add a reference to the issue this PR will solve, if appropriate
• Include changelog additions in one or more commit message bodies between the CHANGELOG_BEGIN and CHANGELOG_END tags
• Normal production system change, include purpose of change in description

NOTE: CI is not automatically run on non-members pull-requests for security
reasons. The reviewer will have to comment with /AzurePipelines run to
trigger the build.

[cocreature]

Thanks! Fixes #6026

[stefanobaghino-da]

Closing as duplicate of #6071