Add generic java client runtime exceptions

[dimas-b]

Nessie has HttpClientException and HttpClientReadTimeoutException, which extend RuntimeException.

While "http" is indeed the "kind" of the Nessie client, having more generic exception names would be beneficial for the overall Nessie java client design and future improvements.

For example: NessieClientException.

[dimas-b]

Conversely, NessieNotAuthorizedException represents HTTP 401 errors, but exists outside of the http client scope in code... Some clarification seems to be in order there,

[snazy]

We could revisit this one for v2 API as well.