[FLINK-30169][python][doc] Adds switcher.json file

This closes apache#21380.

flink-python/docs/_static/switcher.json

@@ -0,0 +1,17 @@
+[
+  {
+    "name": "dev",
+    "version": "master",
+    "url": "https://nightlies.apache.org/flink/flink-docs-master/api/python"
+  },
+  {
+    "name": "1.16 (stable)",
+    "version": "release-1.16",
+    "url": "https://nightlies.apache.org/flink/flink-docs-release-1.16/api/python/"
+  },
+  {
+    "name": "1.15",
+    "version": "release-1.15",
+    "url": "https://nightlies.apache.org/flink/flink-docs-release-1.15/api/python/"
+  }
+]

pom.xml

@@ -1572,6 +1572,7 @@ under the License.
 						<exclude>flink-python/lib/**</exclude>
 						<exclude>flink-python/dev/download/**</exclude>
 						<exclude>flink-python/docs/_build/**</exclude>
+						<exclude>flink-python/docs/_static/switcher.json</exclude>
 
 						<!-- AWS SDK config that does not support license headers -->
 						<exclude>**/awssdk/global/handlers/execution.interceptors</exclude>