Make ClientCredentialsTokenManagementBuilder.Services a public property.

[goldsam]

To enhance the extensibility of this library, consider making ClientCredentialsTokenManagementBuilder.Services a public property.

There are situations where it is desirable to override a subset of the services configured by AddClientCredentialsTokenManagement. In these cases, it would be ideal to support custom AddXXX() extension method to ClientCredentialsTokenManagementBuilder. However, this would require access to the currently private IServiceCollection member.

This change would be consistent with many other DI builders available in core packages, including:

• IHttpClientBuilder.Services
• ILoggingBuilder.Services
• OptionsBuilder<TOptions>.Services