feat(DuoChat): Add default markdown renderer for streaming messages

What does this MR do?

feat(DuoChat): Add default markdown renderer for streaming messages

While we consume streaming messages, we render markdown on the fly in the frontend. Once the message is finally rendered by the backend, we will consume some rendered HTML.

One of the problems we are facing now, that if a streamed message contains code blocks for example, the code blocks might note be closed yet and comments might be rendered as headings:

```yaml
# this is not a headline

will be rendered as:

<p>```yaml</p>
<h1>this is not a headline</h1>

Luckily the CommonMark spec, which marked follows, considers the end of a markdown document as closing the open code block. So we do not need to worry about: gitlab#433338 (closed)

In order to achieve consistent behavior between our current usages of Duo Chat, we add a default markdown renderer to Duo Chat. This will help us solve gitlab-vscode-extension#1227 (closed) more easily while also ensuring that we can quickly fix rendering issues like the aforementioned codeblock issue in a single place.

In order to ensure that the markdown render doesn't "pollute" other components, we lint against imports and add a message that it is only supposed to be used in Duo Chat.

Screenshots or screen recordings

Screen_Recording_2024-02-06_at_13.20.45

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