Explore VaultClient abstraction #942
Description
While adding RestClient support, we noticed that RestOperations served a good purpose, while not being the ideal level of abstraction due to various exposures to path handling and repeated access patterns, especially related to result type handling.
Introducing RestClient immediately clashed with doWithSession methods in lambda usage and that is another hint that we should introduce an intermediate abstraction such as VaultClient to distinguish Vault usage from generic HTTP client usage. Also, a VaultClient exposing a fluent API could limit HTTP usage to Vault needs narrowing down the scope and have hooks for e.g. namespaces, session/unauthenticated usage that are relevant for Vault clients.
Based on VaultClient, we could retrofit the Vault Template API (also the reactive one).