Question: How to add a default middleware to all faraday client instances?

Hi,
How is the correct way to add a default middleware to all faraday client instances?

Example:

My middleware:
```ruby
class MyMiddlware < Faraday::Middleware 
  def call ...
end
```

My clients:
```ruby
conn1 = Faraday.new(url)
conn2 = Faraday.new(url)
```

I expected that all my clients (conn1, conn2) use MyMiddlware as default.