Make API URL dynamic in `maestro validate` output

`maestro validate` command uses production API URL to list the missing builds/boots information.
Make it dynamic and fetch the URL from the settings file i.e. `kci-dev.toml`.

Start with the implementation of the `maestro validate` command and inspect how it currently obtains the API URL. Read the `kci-dev.toml` settings handling, then verify that missing builds and boots are fetched from the configured URL rather than a fixed production endpoint.

Written by the indexing model from the issue text.