[ZEPPELIN-5406] Add detailed explanation for Impersonate on LDAP & Kerberized environments
[ZEPPELIN-5406] Add detailed explanation for Impersonate on LDAP & Kerberized environments

### What is this PR for?
For detailed explanation for how to impersonate on LDAP & Kerberized environments.

### What type of PR is it?
[Documentation]

### Todos
* [ ] - Task

### What is the Jira issue?
https://issues.apache.org/jira/browse/ZEPPELIN-5406

### How should this be tested?
This is about documents update so that the test is not needed.

### Screenshots (if appropriate)

### Questions:
* Does the licenses files need update? No
* Is there breaking changes for older versions? Yes
* Does this needs documentation? Yes

Author: sangrho.lee <sangrho.lee@linecorp.com>

Closes #4132 from Sangrho/add_detailed_explanation_for_impersonate and squashes the following commits:

ebde044ee [sangrho.lee] [ZEPPELIN-5406] Add explanation for Impersonate on LDAP & Kerberized_environments

apache/zeppelin,fogbeam/zeppelin_mirror,apache/zeppelin,apache/zeppelin,zjffdu/zeppelin,jongyoul/incubator-zeppelin,jongyoul/incubator-zeppelin,hammertank/zeppelin,apache/incubator-zeppelin,hammertank/zeppelin,fogbeam/zeppelin_mirror,apache/incubator-zeppelin,zjffdu/zeppelin,prabhjyotsingh/zeppelin,apache/incubator-zeppelin,prabhjyotsingh/zeppelin,jongyoul/zeppelin,zjffdu/zeppelin,hammertank/zeppelin,prabhjyotsingh/zeppelin,apache/incubator-zeppelin,hammertank/zeppelin,fogbeam/zeppelin_mirror,apache/zeppelin,zjffdu/zeppelin,jongyoul/incubator-zeppelin,fogbeam/zeppelin_mirror,jongyoul/incubator-zeppelin,zjffdu/zeppelin,zjffdu/zeppelin,hammertank/zeppelin,fogbeam/zeppelin_mirror,prabhjyotsingh/zeppelin,jongyoul/incubator-zeppelin,jongyoul/zeppelin,apache/incubator-zeppelin,hammertank/zeppelin,fogbeam/zeppelin_mirror,jongyoul/incubator-zeppelin,prabhjyotsingh/zeppelin,apache/incubator-zeppelin,jongyoul/zeppelin,jongyoul/zeppelin,jongyoul/zeppelin,jongyoul/zeppelin,fogbeam/zeppelin_mirror,apache/zeppelin,prabhjyotsingh/zeppelin,zjffdu/zeppelin,prabhjyotsingh/zeppelin,apache/zeppelin,jongyoul/zeppelin,apache/zeppelin,hammertank/zeppelin