Java SDK okhttp dependency version wrong

Describe the issue

https://docs.dapr.io/developing-applications/sdks/java/ states

<dependency>
  <groupId>com.squareup.okhttp3</groupId>
  <artifactId>okhttp</artifactId>
  <version>1.3.1</version>
</dependency>

but the given version of dependency is old and not available on maven central. Therefore the given info is wrong and an obstacle for new users.

URL of the docs

https://docs.dapr.io/developing-applications/sdks/java/

Expected content

A correct version for the dependency. For instance, like mentioned here https://github.com/dapr/java-sdk/issues/515#issuecomment-800435671

I'm not sure what makes the dependency compatible and what not, so I don't know which versions are indeed correct. 4.9.0 just happened to work for me.

I propose we remove OKHTTP as a dependency as part of the work in #626, which means we would use the Java's builtin HTTP client.

/assign