Quickstart documentation

[jiparis]

We want to create a copy-paste quickstart tutorial with the basic steps to get started into chainloop. It must be simple and complete. Something like:

1. install chainloop
2. auth login
3. workflow create
4. api-token create
5. attestation init
6. attestation add
7. attestation push
   To simplify it, we can leverage dynamic contracts and keyless signing.

It must be something easily reproducible by just copying and pasting.