Indicate that max_token_ttl is required for OIDC auth methods

[am-ak]

• Include an example for OIDC auth method
• correct the description of max_token_ttl that it is a required argument for OIDC auth method

[remilapeyre]

Hi @am-ak, thank you very much for reporting this issue. I had missed this when working on consul_acl_auth_mode, it is pretty rare that arguments can be optional or required based on another one.

I kept most of your implementation but migrated the consul_acl_auth_method documentation to the tfplugindocs framework as this is an ongoing migration that I do as we update the documentation of each resources. This is what most of my commits are about, sorry for the noise.

I also updated the example in the documentation to use the one in the Consul documentation.

Thanks for your contribution!