[ANNOUNCEMENT] Dr.Elephant supports SSL enablement

[ShubhamGupta29]

Hi All,
We have made changes to Dr.Elephant so that you all can have a more secure experience with Dr.Elephant. After the SSL enablement

• HTTPS-enabled UIs can make calls to Dr.Elephant.
• Easily add secure authentication and authorization for Dr.Elephant.

PR for changes: #656

[ProbShin]

Thanks @ShubhamGupta29 for the contribution.
If I understand correctly, this PR makes users access Dr.Elephant UI through "HTTPS" SSL protocal by enable keystores to support mtls for authentication.

And correct me if I am wrong. This PR is not for issuing the problem that enables Dr.Elephant to fetch information/metrics from the history server through the "HTTPS" SSL protocol for example when the Hadoop was set under yarn.http.policy is HTTPS_ONLY condition.