Split auto-merge into two inputs

[Logerfo]

One for master->dev and one for release->master.
In order to make it non-breaking, the current input will still be acceptable and should be prioritized. A deprecation warning must be thrown, if possible. The input should be totally deprecated in the next major release.

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[Logerfo]

Gotta find another way through this since #12 already changed the config behavior for another purpose.