[RFC] Research ways to support tagged effects

[chshersh]

Sometimes we want to reuse the same effect implementation but for different environment settings. Examples:

1. Different JWT tokens for different applications.
2. Different DB settings for different databases.
3. Support measuring with either EKG or Prometheus.

So it looks like some effects should be tagged (it's not tagless final anymore).

Initial idea: instead of

class MonadJwt m where

have

class MonadJwt (tag :: k) m where

So in constraints this will look like this:

foo :: (MonadJwt "app1" m, MonadJwt "app2" m) => ...

What do you think?