Replace hard-coded front-end URL by env variable

[iljarotar]

When generating an invite link for a tenant or a project the cli prints an invite link like this:

	_, _ = fmt.Fprintf(c.c.Out, "%s (https://console.metalstack.cloud/organization-invite/%s)\n", resp.Msg.Invite.Secret, resp.Msg.Invite.Secret)

That's not good.

[Gerrit91]

It's the same for the payment service, for which clients need to work with the stripe public token... we probably need an endpoint for the server to retrieve such environmental information?

[majst01]

It's the same for the payment service, for which clients need to work with the stripe public token... we probably need an endpoint for the server to retrieve such environmental information?

This is the asset service

[Gerrit91]

Created a first draft here: metal-stack-cloud/api#201