feat: add support matrix shortcode

[chmouel]

Changes

Added a support matrix shortcode to the policy guide to indicate which Git providers support specific features. This includes GitHub App, GitHub Webhook, Gitea, GitLab, Bitbucket Cloud, and Bitbucket Server.

Update pull_request default template so that the dev can communicate it in the pull_request.

This is how it is used

{{< support_matrix github_app="true" github_webhook="true" gitea="true" gitlab="false" bitbucket_cloud="false" bitbucket_server="false" >}}

And this is how it will look like

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