Default to initializing executable when not specified to cabal init

[m-renaud]

Overview

Default to initializing an executable when running cabal init non-interactively. This is inline with the other Haskell project initialization tools, as well as tools in other languages (such as Rust's Cargo).

This partially addresses #5696.

Rationale

It is more common to want a binary than a library because often one wants to simply play around with an idea then to develop a full fledged library to publish on Hackage. Additionally, the binary case is always more common than the library case because each library is depended upon by 1 or more executables.

Behaviour Change

Before:

cabal init --non-interactive produces a library.

The Library option is choice 1 in the interactive prompt list.

After:

cabal init --non-interactive produces a binary.

The Executable option is choice 1 in the interactive prompt list.

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[23Skidoo]

Merged, thanks!