Make conventionalcommits the default preset

[ondrejsevcik]

Hello,

First of all, I would like to thank you for such an amazing tool.

I was curious whether it would make sense to make the Conventional Commits the default preset.

The Angular preset does not allow for marking breaking changes in a commit message title. It's a major drawback.

There has been some discussion in this PR to make the Conventional Commits the default, so I thought it would be good to bring it up in a separate issue.

Thank you for considering this.

[ondrejsevcik]

I moved the discussion into here semantic-release/semantic-release#3406