Support lodash template for changelog file name

[onemvictor]

This is a proposal for supporting different changelog file per release channel. This can be achieved by supporting lodash template for changelog file name, and expose branch object, like the one available for message parameter of @semantic-release/git plugin. This would have two benifits:

1. Lets the targetted audience recieve the changelog specific to the release channel they are subscribed to.
2. Remove merge conflict when merging between release branches releasing to different channels.