[Chore]: define dashboard api base url using docker env

[peppescg]

Description

In order to allow the users to specify the dashboard base api url (by default it is http://localhost:8989) we can add a docker env DASHBOARD_API_BASE_URL that the users can use to set dashboard api base url in the UI.
Rather than using sed for replace the env var in the js file, we can use envsubst through the index.html that includes the env var used in the UI for handle the API requests.

Additional Context

Discord thread