RSDK-9194: streamline app connection

[purplenicole730]

Jira ticket

Changes:

• added new directory app/
• introduced a ViamClient struct
• made a function CreateViamClient, which takes in api key for credentials
• add unit tests for url and api key formatting

Testing:

• called a proto dataClient and tested with an existing machine
• unit tests

[jckras]

Quick question - how are we going to implement the interfaces for other clients, such as DataClient and BillingClient, here? (In the Python sdk, we define data_client as a property of the ViamClient class). I'm not sure if this is outside the scope of this PR, but I just want to clarify our approach moving forward :)

[jckras]

I left a question about our approach towards building out the other clients w/ respect to ViamClient (but again maybe that is out of scope of this ticket) so LGTM.

[purplenicole730]

Quick question - how are we going to implement the interfaces for other clients, such as DataClient and BillingClient, here? (In the Python sdk, we define data_client as a property of the ViamClient class). I'm not sure if this is outside the scope of this PR, but I just want to clarify our approach moving forward :)

Similarly, the other clients would be part of ViamClient. But we don't have those yet so there's nothing to add. That's what the next tickets are.

[njooma]

I think it would be better if there was an Options struct that contained 2 fields: BaseUri string and Credentials rpc.Credentials. Then, have a func WithOptions that takes in these options.

What I think can be improved from the current version is that baseURL has to always be specified, even if just to be an empty string. Plus, there might be more ways in the future of connecting to app that this allows for.

And nothing is stopping us from making convenience functions like FromApiKey so that the user can use API Keys instead of Options