Catch absolute paths in our docs/code

[idomic]

Reference.

We should add a check to the CI scripts action - it should check absolute paths and fail if it does (can filter on the base URL).

[edublancas]

so for example, if we're on jupysql's repo, we can add base_url = jupysql.ploomber.io to the pyproject.toml, then fail a check if we detect any links that start with the base URL, since those should be relative.