Simplify cmd/zetaclient/start.go

[swift1337]

This file should be simplified and split into several components:

1. config + logger setup
2. tss setup should be encapsulated in tss package
3. zetacore setup
4. orchestrator setup
5. …

For further code readability, we can move the majority of the logic into zetaclient/app/app.go 🆕