Formatting conventions

[AliveDevil]

In #530 I started using :::-fences, due to differentiating markdown extension with code blocks. Before mixing up conventions this should be coordinated with the team.

There are two ways to initiate markdown extensions in fences: ``` and :::. The documentation currently exclusively uses ``` for both - code and markdown extensions, e.g.

```{note}
Content
```

This makes it difficult to easily spot whether a part of the documentation is a code-block, or a special markdown extension. Thus I'd suggest that we review the usage of ```, and use ::: for markdown extensions:

:::{note}
Content
:::