services/horizon/internal/docs: Use full links instead of relative links.

[abuiles]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with name of package that is most changed in the PR, ex.
  services/friendbot, or all or doc if the changes are broad or impact many
  packages.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated any docs (developer docs, .md
  files, etc... affected by this change). Take a look in the docs folder for a given service,
  like this one.

Release planning

• I've updated the relevant CHANGELOG (here for Horizon) if
  needed with deprecations, added features, breaking changes, and DB schema changes.
• I've decided if this PR requires a new major/minor version according to
  semver, or if it's mainly a patch change. The PR is targeted at the next
  release branch if it's not a patch change.

What

Use full URL for some links.

Why

Some of the fixed links don't work today in the production docs and also fixes some links added in #1887

Known limitations

N/A

[ire-and-curses]

Hey! There's a couple of reasons we've been using relative links:

1. It decouples the docs from the deployment domain (i.e. we aren't hard-coding developers.stellar.org everywhere)
2. It allows the doc links to work when viewed on Github.

I do agree that some of the links were broken (this is my bad, I promised to fix them and didn't). But this could be resolved by just changing the relative path.

What do you think? My preference is to use relative links and just fix the paths, unless there are other pros to the full paths that I didn't surface here.

[abuiles]

@ire-and-curses I agree with you, I prefer relative links rather than full links. Actually we might not need this change, we thought using ../../../guides will break under /developers but I just tested one of the links in master using this schema and it works. So it's all good!

I'll open a different PR to fix the broken links to XDR.