DOC: add pandas-gbq and related db-dtypes packages to ecosystem (#59491)

* DOC: add pandas-gbq and related db-dtypes packages to ecosystem

As of pandas 2.2.0, pandas-gbq functionality is fully separated, so I think now would be a good time to introduce it as part of the "ecosystem".

db-dtypes was built for use from pandas-gbq but should be applicable more generally.

* fix pandas-gbq link

web/pandas/community/ecosystem.md

@@ -360,6 +360,13 @@ Deltalake python package lets you access tables stored in
 JVM. It provides the ``delta_table.to_pyarrow_table().to_pandas()`` method to convert
 any Delta table into Pandas dataframe.
 
+### [pandas-gbq](https://github.com/googleapis/python-bigquery-pandas)
+
+pandas-gbq provides high performance reads and writes to and from
+[Google BigQuery](https://cloud.google.com/bigquery/). Previously (before version 2.2.0),
+these methods were exposed as `pandas.read_gbq` and `DataFrame.to_gbq`.
+Use `pandas_gbq.read_gbq` and `pandas_gbq.to_gbq`, instead.
+
 ## Out-of-core
 
 ### [Bodo](https://bodo.ai/)
@@ -513,6 +520,13 @@ Arrays](https://awkward-array.org/) inside pandas' Series and
 DataFrame. It also provides an accessor for using awkward functions
 on Series that are of awkward type.
 
+### [db-dtypes](https://github.com/googleapis/python-db-dtypes-pandas)
+
+db-dtypes provides an extension types for working with types like
+DATE, TIME, and JSON from database systems. This package is used
+by pandas-gbq to provide natural dtypes for BigQuery data types without
+a natural numpy type.
+
 ### [Pandas-Genomics](https://pandas-genomics.readthedocs.io/en/latest/)
 
 Pandas-Genomics provides an extension type and extension array for working