Determine from the API if an Auth Backend is a plugin

[michaeljs1990]

Is your feature request related to a problem? Please describe.
I am trying to add support so that terraforms vault provider can manage custom auth plugins. However the one way that I see to determine that has been removed and now returns nothing. It looks like before a none blank PluginName provided would have done the trick however now that always returns an empty string.

The reason this is important is because based on if this is a plugin or not the terraform state would need to be written differently since plugin path is required to enable the plugin. Additionally type plugin is required to be provided when enabling but when you list the auth backends it's type comes back out as "plugins-random-name".

Describe the solution you'd like
I don't much care what the solution is but it would be nice to be able to manage custom vault plugins in terraform. Right now I only care about the auth backend but this might apply more widely as well. Something like "IsPlugin: true/false" would be nice to return via the API.

Describe alternatives you've considered
Fork the code.

Does some other trick exist to determine when a auth method is a custom provided plugin that I am missing? This first came up in hashicorp/terraform-provider-vault#54.

[michaeljs1990]

hrm, before anyone spends any time on this I found #5536. Taking a closer look but it looks like this isn't needed anymore but the docs needs to be updated a bit since they still reference plugin_name most places.

[michaeljs1990]

The above issue does fix this. I'll open a PR to clean up the docs a bit so I don't feel like I wasted too much time :)