Fix okhttp vulnerability CVE-2021-0341

Summary:
GitHub detected a critical security vulnerability (CVE-2021-0341) in the
com.squareup.okhttp3:okhttp dependency used in Java SDK examples.

What broke:
OkHttp versions < 4.9.2 are vulnerable to CVE-2021-0341, where the library
fails to properly verify hostnames during TLS certificate validation. This
could allow man-in-the-middle attacks against HTTPS connections made by the
Java Business SDK examples.

How we're fixing it:
Bumped okhttp from 3.9.1 to 4.12.0 in both pom.xml files:
- codegen/templates/java/examples/pom.xml (facebook-business-sdk-codegen)
- sdk/servers/java/release/examples/pom.xml (facebook-java-business-sdk)

Version 4.12.0 is the latest stable 4.x release, well above the minimum
fix version of 4.9.2.

Differential Revision: D99888404

fbshipit-source-id: 64e8359f7b9afdf66b22f2b6c6f903b20cf20aaa

Author: satwikareddy3

examples/pom.xml

@@ -257,7 +257,7 @@
     <dependency>
       <groupId>com.squareup.okhttp3</groupId>
       <artifactId>okhttp</artifactId>
-      <version>3.9.1</version>
+      <version>4.12.0</version>
     </dependency>
     <dependency>
       <groupId>com.google.guava</groupId>