[Refactor] Introduce Policy Resolver

[codelipenghui]

Is your enhancement request related to a problem? Please describe.
In Pulsar, there are multiple level policies such as topic level policy, namespace level policy, broker level policy. Therefore we have to merge the different level policies. The priority is the topic level > namespace level > broker level.

The user should get the real policy that set. For example, if the broker level enables the topic auto-deletion and users don't set this policy at the namespace level policy, users should get the topic auto-deletion does not present at the namespace level

Currently, we don't have a unified mechanism to handle the policies in Pulsar. So it's better to add a Policy Resolver to optimize current implementation.

The Policy Resolver should contain the following functions

1. merge and get the policy
2. get the policy without merge(used for policy query from the user).