Define the "value" in a Variable Query Parameter which is defined on the interface

**Description**
I've defined a query parameter on an interface like this:
``` C#
public interface IApi
{
[Query("api-version")]
string ApiVersion { get; set; }

[Get("users")]
Task> GetUsersAsync();
}
```

What I would to do is set the **value** for this Query Parameter like this:
``` C#
public interface IApi
{
[Query("api-version", "abc")]
string ApiVersion { get; set; }

[Get("users")]
Task> GetUsersAsync();
}
```

This makes the code more clean then just adding `?api-version=abc` to every method like described here: https://github.com/canton7/RestEase#constant-query-parameters

**Version Info**
- RestEase version: [1.5.5]

Start with the constant query parameters documentation linked in the issue and trace how the Query attribute is handled for interface properties and methods. The change is done when a query parameter declared on an interface can express a constant value as shown, with the existing behavior preserved for parameters without one.

Written by the indexing model from the issue text.