Replace many absolute URLs with root-relative URLs

[thomasrebele]

This PR replaces the absolute URLs (e.g., https://hive.apache.org/community/resources/hivedeveloperfaq) with root-relative URLs (/community/resources/hivedeveloperfaq). This makes it easier to navigate through the site when testing the site locally with hugo server.

I manually checked the links and fixed some minor nearby formatting issues.

[zabetak]

Would it be possible to use the ref shortcode for the URLs? Hugo can raise some error/warning when a path cannot be resolved which can be very helpful to avoid broken URLs.

[thomasrebele]

On the ref shortcode page there's a warning

When working with Markdown this shortcode is obsolete. Instead, to properly resolve Markdown link destinations, use the embedded link render hook or create your own.

I checked a md file of the Hugo documentation, and it does not use ref. Instead it defines the references at the end of the md file.

There are ways to verify the links with some Hugo code. I've found a discussion on Hugo's discourse, which includes a link to a tutorial. However, I think it's out-of-scope to implement this functionality in this PR.

[zabetak]

I went through the diff and everything LGTM! Will merge soon.

[thomasrebele]

I've imported the link validator, and it seems to work, though we would need to remove the ref shortcuts. See the PR.