For JWT authentication, the claims to verify now may be provided as a list of maps:
```
[
    {
        name = "claim_name"
        value = "${username}"
    },
    ...
]
```

Expected values now treated as templates, uniformly with the oither authenticators.
They now allow arbitrary expressions including `${username}` and `${clientid}` variables.
Previousy, only fixed `"${username}"` `"${clientid}"` values were supported for interpolation.

Improved the documentation for the `verify_claims` parameter.