Prevent deprecation of AppServerOrSAMLIdPServiceProvider from being a breaking change

[gzdunek]

Closes #39031

In #38709 the types KindAppOrSAMLIdPServiceProvider and AppServerOrSAMLIdPServiceProvider were deprecated.
Unfortunately, this was also a breaking change for v15 clients because SAML providers started to be sent as types.SAMLIdPServiceProvider instead of types.AppServerOrSAMLIdPServiceProvider.

AFAIK the only thing we need to fix is the paginated resources response.
This can be done by checking the client version and sending a compatible response.

[gzdunek]

I just learned from @espadolini that we should avoid checking the client version, I will try to send the same resource twice from the server, the clients should support only the new or old resource.

[gzdunek]

Okay, I realized that returning the same resource twice won't work. The new types.KindSAMLIdPServiceProvider resource will be sent starting from v16 and there are places in the code that return an error when they receive an unknown resource type (for example, web/apiserver).
So, I have to stick to checking the client version, otherwise auth v16 may not work with proxy v15.