feat: report: Add markdown report template to contrib.

[PedroMSantosD]

Description

Add a markdown template for scan reports. Should help making the outcome of the trivy scan part of the comments on a github-actions based pipeline

Related issues

• Close #XXX

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[CLAassistant]

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[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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Pedro Santos seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[knqyf263]

We're afraid that we don't plan to accept more templates.
#3202 (comment)