Multi User Support

[@amor71]

Is your feature request related to a problem? Please describe.
Currently, the framework supports a single user and a single tradeplan.toml file. This file is read each time the platform starts. It is quite convenient for a single user running trades for him/herself.

The required change address two related issues:

1. Support several users, running different strategies in parallel,
2. Move beyond the tradeplan.toml file allowing different plans for different users

Describe the solution you'd like

1. extend the Portfolio table to include additional details such as broker & external account id,
2. extend trader(s) to support trading on behalf of others,
3. extend DB model to allow setting up a trade-plan per user

[github-actions]

Stale issue message

[@amor71]

v 4.10 released