support pegasus connect zookeeper which one use kerberos

[GehaFearless]

Feature Request

Is your feature request related to a problem? Please describe:
In our business, pegasus cluster need to connect zookeeper which use kerberos protocol. I want support it.

Describe the feature you'd like:
Before version 2.3, we support it by customized zookeeper c client which convert java client use JNI. From version 3.7.0, zookeeper support c client use kerberos. I want to introduce it for pegasus.
Through my test, two parameter is required for 'zookeeper_init_sasl' different from 'zookeeper_init' which func get handle that represents a connection to the ZooKeeper service.

• Current implementation

_handle = zookeeper_init(zookeeper_session_mgr::instance().zoo_hosts(),
                         global_watcher,
                         zookeeper_session_mgr::instance().timeout(),
                         nullptr,
                         this,
                         0);

• Support Kerberos implementation

zoo_sasl_params_t sasl_params = { 0 };
sasl_params.service ="zookeeper"
sasl_params.mechlist = "GSSAPI";
_handle = zookeeper_init_sasl(zookeeper_session_mgr::instance().zoo_hosts(),
                              global_watcher,
                              zookeeper_session_mgr::instance().timeout(),
                              nullptr,
                              this,  
                              0,
                              NULL,
                              &sasl_params);

When we have completed the above initialization and own valid kerberos ticket, we finised this job. How to get valid kerberos ticket already implemented on our code (kinit_context.cpp: https://github.com/XiaoMi/rdsn/blob/fc41809ce1622a47a535a2316df91d4d626f35ed/src/runtime/security/kinit_context.cpp).

Finally, we need to add some configuration items:

1. FLAGS_enable_zookeeper_kerberos
2. FLAGS_zookeeper_kerberos_service_name: It's always zookeeper, but it can change more

by the way，this issue is same as XiaoMi/rdsn#85

[Smityz]

It's a good idea for pegasus to adapt to various environments. can you pull a request for the function?