[Docs] Use relative internal links in the sphinx docs

[asfimport]

There are a lot of hardcoded urls referencing non-sphinx documentations across the generated HTML files, couple of examples:

• https://arrow.apache.org/docs/r/

• https://arrow.apache.org/docs/js/

• https://arrow.apache.org/docs/c_glib/

• https://arrow.apache.org/docs/java/reference/

  Using the new versioned docs the https://arrow.apache.org/docs/5.0/java/index.html links should point to https://arrow.apache.org/docs/5.0/java/reference/ instead of https://arrow.apache.org/docs/java/reference/

  cc @jorisvandenbossche

Reporter: Krisztian Szucs / @kszucs

Related issues:

• [Docs] Ensure links to non-sphinx parts of the docs are relative instead of absolute (duplicates)

_{Note: This issue was originally created as ARROW-14497. Please see the migration documentation for further details.}

[asfimport]

Joris Van den Bossche / @jorisvandenbossche:
I had already opened ARROW-14496 for this, so closing as a duplicate