docs: fix intersphinx mapping for arrow-java reference (apache#3908)

Author: lidavidm

docs/source/conf.py

@@ -147,6 +147,7 @@ def setup(app):
 
 intersphinx_mapping = {
     "arrow": ("https://arrow.apache.org/docs/", None),
+    "arrowjava": ("https://arrow.apache.org/java/current/", None),
     "pandas": ("https://pandas.pydata.org/docs/", None),
     "polars": ("https://docs.pola.rs/api/python/stable/", None),
     "python": ("https://docs.python.org/3", None),

docs/source/format/related_work.rst

@@ -68,7 +68,7 @@ a particular system; or 2) could be used to implement such access.
   with application-specific extension points but without any higher
   level semantics.
 
-:external+arrow:doc:`Arrow JDBC <java/jdbc>`
+:external+arrowjava:doc:`Arrow JDBC <jdbc>`
   A Java submodule, part of Arrow/Java, that uses the JDBC API to
   produce Arrow data. Internally, it can read data only row-at-a-time.