[META] Admin user should have a custom non-hardcoded password

[DarshitChanpura]

High-level Idea

As one of the outcome of this spike, this feature-request is to replace admin password, which is currently hard coded in demo configuration, with a custom password. If none is provided, a random password should be generated and set for admin user. Here is the intended design:

sequenceDiagram
    participant User
    participant Cluster
    participant Script

    User->>Cluster: Start cluster setup with security plugin
    Cluster->>Script: Execute demo script
    alt User provided password
        Script->>Script: Search for user provided password
    else No password provided
        Script->>User: Script execution fails as no password provided
    end
    Script->>Cluster: Continue with demo script execution
    alt Demo script execution successful
        Script->>Cluster: Notify demo script execution complete
    end
    Cluster->>Cluster: Continue with security plugin configuration

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Acceptance Criteria

• Update the demo configuration install script to accept a custom password for admin user
  - [ ] If no custom password is provided, the script should generate a new one, set it for admin and let the end user know (no longer considered)
• This change works with at-least one of the supported OpenSearch distributions

Exit Criteria

• [Question] Should the demo install script be translated to Java tool? #3632
• Extracting install_demo_configuration script to a standalone Java Tool #3633
• Implement tests to verify changes to default admin credentials #3636

Would like

• Implement a password validation logic to ensure that a weak password is not supplied as custom password.

[stephen-crawford]

[Triage] This is the last of the meta issues tracking progress removing the use of default credentials in the cluster. Marking as triaged given clear action items and exit criteria.

[DarshitChanpura]

Closing this as all sub-tasks are now complete.