Generate admin password on startup

[peternied]

Use case:

On startup the admin user is created with a random password.

Acceptance Criteria:

• The password is printed into the console output.
• The password is printed into a text file on disk that can be read via automation
• The by providing the username/password through basic auth an debug message appears in the opensearch log showing they authenticated.
• The user/password does not need to persist through service restart or be shared over multiple nodes.
  • When password updating/setting APIs have been created use these.
• The password that is generated conforms to a publicly used standard.

[peternied]

To see a good example of this checkout how Jenkins does this during its startup workflow https://www.jenkins.io/doc/pipeline/tour/getting-started/