Support delegating BearerTokenResolver

[franticticktick]

Need to add support for retrieving tokens from different headers in one component. This is a common case when a project has multiple authentication schemes. For example, in ProviderManager there are two providers, but one gets the token through DefaultBearerTokenResolver and the other from a non-standard header like -X-Authorization.
For example, component DelegatingBearerTokenResolver:

    @Override
    public String resolve(HttpServletRequest request) {
        return delegates.stream()
                .map(d -> d.resolve(request))
                .filter(Objects::nonNull)
                .findAny()
                .orElse(null);
    }

[franticticktick]

It also makes sense to make a DelegatingServerAuthenticationConverter for different authentication schemes. What’s interesting is there is no way to change the authorizationPattern in the ServerBearerTokenAuthenticationConverter, which prevents this component from being used for non-standard authentication schemes.

[jzheaux]

I think a DelegatingServerAuthenticationConverter would be nice, @CrazyParanoid. Can you submit a PR for it?

[franticticktick]

Added DelegatingBearerTokenResolver. I see that DelegatingServerAuthenticationConverter was added in another PR.