Migrate vault client from okhttp to the quarkus rest client

[vsevel]

Description
The Vault extension uses okhttp to connect to vault. It would be much better to rely on the default quarkus jax-rs client.
This feature request is related to #2897 (comment) and #2897 (comment).
The rest client must be usable from cdi beans (such as VaultKvService) and the vault config source. The challenge is that the jax-rs client requires configuration to be initialized, and so using the quarkus rest client from the config source gets us in an infinite recursive loop.
Once we can use the rest client from the config source, we will be able to throw away several classes from the vault extension (OkHttpVaultClient and associated classes). It will however make us loose the ability to refer to a pem file directly (which is convenient in kubernetes), and force the use of a truststore (and add initialization complexity, such as dynamically-creating-java-keystores-openshift)