Hook system improvements

[endgame]

While writing an example that uses hooks, I noticed that they were very hard to use correctly, and reasonable-looking code would silently ignore the request type you think you're hooking into.

We should provide {add,remove}Hook{,_} variants which are specialised to each hook type and are harder to misuse:

1. addHookFor and addHookFor_ should be moved to the bottom of the file and marked {-# DEPRECATED #-} with a message recommending the hook-specific functions, and promising removal in 2.2. The export list for Amazonka.Env.Hooks should have a -- * section for deprecated functions.
2. addAWSRequestHook should be renamed to addRequestHookFor, and addAWSRequestHook should remain as a {-# DEPRECATED #-} alias, also scheduled for removal in 2.2.
3. addAWSRequestHook_ should be deprecated and scheduled for removal in 2.2.
4. removeHooksFor and removeHooksFor_ should be moved to the bottom of the file and deprecated, much the same as №1.
5. For each field in the Hooks record (example requestRetry) that has a forall a, we should have:
   • An add-for function for this hook: addRequestRetryHookFor :: forall a b. Hook_ (Request a, Text, Retry.RetryStatus) -> Hook_ (Request b, Text, Retry.RetryStatus) -> Hook_ (Request b, Text, Retry.RetryStatus) = addHookFor_ @(Request a, Text, Retry.RetryStatus)
   • A remove-for function for this hook: removeRequestRetryHookFor :: _ = removeHookFor_
6. Haddocks for each new function from №5
7. Export these in a new -- ** Functions for specific hooks first, with an explanatory note:

   -- ** Functions for specific hooks
   -- $functions-specific-hooks (say that the type application for these is the AWS Request type e.g. `@S3.GetObject`.)
   addRequestHookFor,
   removeRequestsHooksFor,
   ...
   -- ** Functions for arbitrary hooks
   -- $functions-arbitrary-hooks
   noHook,
   noHook_,
   addHook,
   addHook_,
   ...

[endgame]

@dalpd as discussed at ZuriHac