Think through caching config

[cbrit]

It's been unofficially decided ocular doesn't really need a cli because it's redundant with lens. However, one really useful thing about the lens cli is that it caches chain registry config data locally. Ocular should probably have this capability in case the registry becomes inaccessible such as during a Github outage.

Ocular could cache config in a local file when a chain client is first constructed so that future construction of clients for that chain wouldn't need to make calls to the registry. We may need to think about some kind of policy around making sure the config doesn't get stale like if endpoints are updated in the registry. Alternatively we could leave this to the user. Perhaps some kind of way to configure the behavior at client construction time (a method like ChainClient::new_with_options()?). This issue for starting a discussion.