Update the management documentation for TypeDB Cluster #621

We should document the "authentication" and "encryption" features in the docs. They should be located under the "Management" section.

Authentication
The authentication page should cover the following:

1. How does the authentication work
2. How to manage user accounts (creating, viewing, updating, and deleting)

Encryption
The encryption page should cover the following:

1. How does the encryption work:
   a. For external communication, ie., client-server
   - using the development certificate
   - using self-generated certificate
   - using one generated by established providers such as letsencrypt.org
   b. For internal communication, ie., between one server to another)
2. How to configure / generate the certificate for external communication
3. How to configure / generate the certificate for internal communication