[RPC-Spec-V2] Backport changes to chainHead

[lexnv]

Implement the following changes to the chainHead class of RPC methods:

• Change the chainHead functions to have proper limits json-rpc-interface-spec#66

The chainHead_follow is now responsible for generating the result of the other methods:

• chainHead_follow events / errors are extended to announce blocks and results of other methods
• chainHead_storage, chainHead_call, chainHead_body are plain methods that return an operation ID
• chainHead_follow produces the response of the provided operations
• ongoing operations can be canceled by a new method chainHead_stopOperation
• chainHead introduces a minimum 16 number of ongoing operations after which the limitReached event is produced

// @paritytech/subxt-team

### Tasks
- [ ] https://github.com/paritytech/substrate/issues/14222
- [ ] https://github.com/paritytech/substrate/issues/14637
- [ ] https://github.com/paritytech/substrate/issues/14638
- [ ] https://github.com/paritytech/substrate/issues/14639
- [ ] https://github.com/paritytech/substrate/issues/14640