[Dubbo-6481]Fix Extended LoadBalance ran 2 times during service call

[zhangyz-hd]

ZoneAwareClusterInvoker在选择注册中心时，使用配置的loadbalance，而不使用service属性中的loadbalance。

What is the purpose of the change

To fix #6481

Brief changelog

当配置了多个注册中心时，ZoneAwareClusterInvoker会使用LoadBalance对多个注册中心进行一次筛选。
原是使用当前服务对应的loadbalance，当服务配置了自己的loadbalance时，ZoneAwareClusterInvoker就错误选择了服务的loadbalance区筛选注册中心。
现改为由LOADBALANCE_AMONG_REGISTRIES配置项的loadbalance（默认random）。

Follow this checklist to help us incorporate your contribution quickly and easily:

• Make sure there is a GITHUB_issue field for the change (usually before you start working on it). Trivial changes like typos do not require a GITHUB issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
• Format the pull request title like [Dubbo-XXX] Fix UnknownException when host config not exist #XXX. Each commit in the pull request should have a meaningful subject line and body.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• Run mvn clean install -DskipTests=false & mvn clean test-compile failsafe:integration-test to make sure unit-test and integration-test pass.
• If this contribution is large, please follow the Software Donation Guide.