cli: instantiate viper and swagger client in root command instead of using singletons

[BrunoRosendo]

Currently, some tests are having problems because the client and viper were used as singletons. It'd be better to instantiate them once in newRootCmd() and pass them to the commands that need them, facilitating the way unit tests are done as well.

[BrunoRosendo]

The problem with this approach is that the api client uses viper to get the server URL. This means we'll have to pass the viper instance through every command to then pass it to the client, which probably defeats the point of the issue.

We should find another solution for the api client. Maybe we could instantiate the api client in root and pass the client to all the commands

[BrunoRosendo]

Draft PR #119 showcases how this could look like and initiates a discussion on whether it's worth it or not