Allow resources to be read in different Fs according to data in context

In ResourceManager.Read, add `ctx context.Context` as the first parameter. Then, update corresponding resource descriptors so that FindResources will use the context to determine if the Fs can be used or not.

* Background: We want to let resource to be overridable by app fs depending on some runtime factors, such as project plan.

Related to [https://github.com/authgear/authgear-server/issues/3886](https://github.com/authgear/authgear-server/issues/3886)

Start by tracing ResourceManager.Read and FindResources, then inspect the corresponding resource descriptors that choose an Fs. Update the read path to accept context and make descriptor selection honor runtime context; done means resources can be overridden by the app Fs according to context without breaking existing callers.

Written by the indexing model from the issue text.