rcmgr: Rename resource manager to resource accountant

... or something else.

The resource manager doesn't manage resources. It simply tracks the current usage of resources along with their predefined limits. It returns an error if current usage goes above the limits. This is more like an accountant then a manager. Calling it a manager makes it seem like this does more than it really does. It also makes it seem that this component is in charge or resource management, when, in fact, it's up to [each protocol](https://docs.libp2p.io/concepts/security/dos-mitigation/#incorporating-dos-mitigation-from-the-start) to be resource aware. Or to leverage the OS (containers, cgroups).

The resource manager is kind of like a bank account. I can try to withdraw $10, and that will probably work. But if I try to withdraw a million dollars, it'll certainly fail. My bank account doesn't manage my money and it doesn't prevent me from spending all my money on a single bored ape.

Start by locating the resource manager entry point and all references to its current name. Confirm the replacement name with maintainers, then update the component and its references consistently; done means the terminology reflects resource accounting without changing the stated usage-limit behavior.

Written by the indexing model from the issue text.