Investigate if a GetterClient still makes sense

[haerdib]

Current issue

Previously, a lot of input parameters were necessary to define the Api struct. That's no longer the case with our Config. So instead of directyl implementing a GetterClient, it should be looked into, if there's still a benefit to a GetterClient.

Original text

Or similar. This way, all the unnecessary parameters, like signer, extrinsic params and such don't need to be defined in case on only needs to query node but not send extriniscs.

Check out the related discussion in #357.