openbao provider

[KoenDierckx]

We are using openbao as our credential provider. It is the open source fork of vault.
By using the vault provider and the vault cli, we can access our openbao server via fnox

But having direct support for openbao, and its cli "bao" would be nice

Technical quick solution, perhaps add a config option to the vault provider, to choose the client binary
But perhaps creating a totally new provider is the best long term option, although that would mean maintaining vault/openbao features in 2 providers...