Add support for FlattenAudience

[marhag87]

I am trying to mock a service that unfortunately doesn't follow spec. The JWT library you use has support for flattening the audience, but this is not exposed in your project. I was able to add the following code to https://github.com/murar8/local-jwks-server/blob/main/internal/token/token.go#L66 to fix my problem locally, but I am not good enough at GO to make a pull request. t.Options().Enable(jwt.FlattenAudience)
The line was taken from the following example in the library: https://github.com/lestrrat-go/jwx/blob/develop/v3/examples/jwt_flatten_audience_example_test.go

Thank you for a great project!

[murar8]

Hi @marhag87, makes sense, let me take a look.