Fix resource server autoconfig to not require OAuth2 client

[therepanic]

In this commit, we remove the InMemoryClientRegistrationRepository class from the OAuth2ResourceServerAutoConfiguration clause, after which we become independent of the OAuth2 client side.

Closes: gh-329

[therepanic]

As stated here, this class was copied:

// All copied from Spring Boot
// (https://github.com/spring-projects/spring-boot/issues/43978), except the
// 2 @Beans of type AuthenticationProcessInterceptor

However, to be honest, I didn't quite figure out where exactly it came from. Therefore, I don't quite understand why the @ConditionalOnClass class InMemoryClientRegistrationRepository was inserted. In fact, the server part should be completely isolated from the client part. In addition, the deletion was completely successful and all tests passed.

I also wrote a small local test (I didn't attach it because I thought it wouldn't be entirely relevant) that somehow checks whether we are isolated from the client part when starting the server resource. I did something like this:

private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
    .withClassLoader(new FilteredClassLoader(“org.springframework.security.oauth2.client”))
    .withConfiguration(
        AutoConfigurations.of(GrpcSecurityAutoConfiguration.class, OAuth2ResourceServerAutoConfiguration.class))
    .withUserConfiguration(TestConfig.class);

And everything went well, in principle. Without this change, the test given in main fails. In general, I don't quite understand why this dependency was inserted, and it seems to me that it's some kind of bug.