Relative URLs in welcome dashboard markdown

[marnovo]

Just noticed when running source{d} CE on a GCP cluster that the URLs in the welcome dashboards are not relative, but hard-coded with local server IP. E.g.:

### Before you get started

You can come back to this Welcome dashboard at any point for references and information:
via browser navigation, [URL](http://127.0.0.1:8088/superset/dashboard/welcome-local/) or in the [list of dashboards](http://127.0.0.1:8088/dashboard/list/).

You can refer to the [source{d} CE full documentation](https://docs.sourced.tech/community-edition/) for more in-depth content.

### Visualize your data on dashboards

- **[Explore source code-related use cases & metrics](http://127.0.0.1:8088/superset/dashboard/1/)**

_Note: You may also create your own metrics, charts & dashboards._

_Note: Very large datasets may eventually cause timeouts loading charts. If this happens, refresh a few at a time._

I guess just removing that would make them relative? Worth checking in the code if this affects anything other than the welcome markdown files.