Cleaning up connection and v2 secrets

[john-delivuk]

We're currently experimenting with viperx / vault provider. Over the course of working with this the last few days I've noticed a few things I addressed in this PR and I wanted to share. I don't think this is complete at this time, but wanted to open it for feedback. I'd like to move in the same direction as the project rather than fork if possible.

High level changes

1. Relying on the Vault SDK for the connection values rather than parsing. My opinion is we should allow overriding but I think we should change the interface for AddRemoteProvider method to accept a config struct for the provider, that it will attach to that provider instantiation.
   Whoops, just realized this is part of Viper proper. Thinking about what a better solution would be.
2. Allowing parsing of both kv2 structs and kv1 as well as all other secrets engines. In all other except kv2, your response is like the following

{
	"data": {
		"serect1": "somethingsecret",
		"serect2": "somethingelsesecret"
	}
}

kv2 looks like

{
	"metadata": {
		"version": 1
	},
	"data": {
		"data": {
			"serect1": "somethingsecret",
			"serect2": "somethingelsesecret"
		}
	}
}

Right now I'm making that choice based on if data is found, but I think it would be best to validate both data and metadata are present before assuming kv2.

Would love your feedback on these, or gauge your interest on moving forward. Happy to help with making this a more powerful plugin.

[john-delivuk]

due to the inactivity here we're going to fork.