Make alert messages in issue more helpful

Hi there!

I've just implemented the GitHub Actions at a company, and there are some things which are cumbersome around the workflow. This issue specifically addresses the "Issue" created and missing information in it.

1. The individual alerts are hard to understand without more context.

   To solve this, I would add information about the severity and add a link to the description for each alert. I already provided a PR (#43) for this.

2. It's hard to see which alerts are more and which are less important

   For this, I would group the alerts by severity.

3. There's no good summary for the overall report

   Here, I would recreate the summary table from the markdown report and add it to the top of the issue.

In addition, I would like to add a testing framework and some tests to be able to more confidently work on the code.

Start by reviewing the existing issue-generation flow and PR #43, which already addresses additional alert context. Then identify where severity grouping and the summary table belong, and determine how a testing framework can cover the changes. Done means the issue includes clearer alert details, severity grouping, an overall summary, and tests.