[fix] [build] rename schema_example.conf to schema_example.json (#21447)

### Motivation

Since the files will be checked for `LICENSE` whose name is a suffix with `.conf`. But we can not add a LICENSE definition for the file `schema_example.conf` because it is a `JSON` file.

Note: the file `schema_example.conf` is only used for the integration test `CLITest.java`.

### Modifications

Rename `schema_example.conf` to `schema_example.json`.

(cherry picked from commit 517961e749120e8f8cb5217a56cf37bbb50183ec)
diff --git a/conf/schema_example.conf b/conf/schema_example.json
similarity index 100%
rename from conf/schema_example.conf
rename to conf/schema_example.json
diff --git a/pom.xml b/pom.xml
index 33176ee..f688fa5 100644
--- a/pom.xml
+++ b/pom.xml
@@ -1648,7 +1648,7 @@
                 <exclude>**/ByteBufCodedOutputStream.java</exclude>
                 <exclude>**/ahc.properties</exclude>
                 <exclude>bin/proto/*</exclude>
-                <exclude>conf/schema_example.conf</exclude>
+                <exclude>conf/schema_example.json</exclude>
                 <exclude>data/**</exclude>
                 <exclude>logs/**</exclude>
                 <exclude>**/circe/**</exclude>
@@ -1773,7 +1773,7 @@
             <exclude>**/requirements.txt</exclude>
 
             <!-- Configuration Templates -->
-            <exclude>conf/schema_example.conf</exclude>
+            <exclude>conf/schema_example.json</exclude>
             <exclude>**/templates/*.tpl</exclude>
 
             <!-- helm files -->
diff --git a/tests/integration/src/test/java/org/apache/pulsar/tests/integration/cli/CLITest.java b/tests/integration/src/test/java/org/apache/pulsar/tests/integration/cli/CLITest.java
index 7e8f554..f13a4dc 100644
--- a/tests/integration/src/test/java/org/apache/pulsar/tests/integration/cli/CLITest.java
+++ b/tests/integration/src/test/java/org/apache/pulsar/tests/integration/cli/CLITest.java
@@ -402,7 +402,7 @@
             "upload",
             topicName,
             "-f",
-            "/pulsar/conf/schema_example.conf"
+            "/pulsar/conf/schema_example.json"
         );
         result.assertNoOutput();