[FEATURE] Support GitHub like Markdown Admonitions

[linawolf]

See https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts

Resolves #1089

[jaapio]

With respect to backward compatibility I think we should add the AdmonitionNode in guides and make the one in RST extend from that one.

Same applies to the AdmonitionNodeRenderer that one should be moved to guides and extended in RST for BC purposes.
Otherwise guides will not work with just markdown installed.

Regarding the blockQuoteParser, I think we might need a custom extension for the commonmark library to support this properly. But that's more a nice to have. That we can revisit later.

[linawolf]

I moved extended the classes in the rst. Duh, completely forgot about the node renderer

[phpdoc-bot]

💚 All backports created successfully

Status	Branch	Result
✅	1.x

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