New docs: make all URLs in MDX (markdown or JSX) root relative

[lunelson]

Currently, the links to "prototype an assistant" from the Installation page at https://rasa.com/docs/rasa/installation are written relatively, which means that
if you are on the trailing slash version of the URL (https://rasa.com/docs/rasa/installation/, which Netlify treats equally to the non-trailing-slash URL), and you follow a link to prototype-an-assistant it is broken, because the browser looks for a sibling of installation/index.html rather than a sibling of installation.html.

Unfortunately we have to work with trailing slashes, due to limited choices in redirection patterns with Netlify, so we need to note in our style guide that links must be root-relative, i.e. /docs/rasa/prototype-an-assistant at all times.

Alternative: can the CI be configured to catch these?

[erohmensing]

@m-vdb i believe this was automated with the useBaseUrl ci check, right?

[m-vdb]

yes this is fixed, we can close this 👍