Decrease stuttering in providers

[epels]

All providers live in their own package, but many types also contain the provider name.

The result is code like this:

provider := messagebird.NewMessageBird(messagebird.MessageBirdConfig{
    AccessKey: "YOUR_ACCESS_KEY",
    // ...
})

I'd like to propose dropping these redundant prefixes in type names, which looks a lot cleaner:

provider := messagebird.New(messagebird.Config{
    AccessKey: "YOUR_ACCESS_KEY",
    // ...
})

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The messagebird package is only an example - this applies to nearly all other providers.

This is obviously a breaking change, so I'll set the milestone for this to v1.0.0.