add dev type to towncrier to reduce use of skip news tag

[onerandomusername]

We use the skip news tag a lot recently, as the changelog is mainly for end users. What we can do (and would probably make more sense) is to use a category on towncrier with showchanges=False. This means our changelog would still be validated, but in the final end-user changelog, that aspect would not be built. We can, however, build that segment into our development changelog when we build it when not on a release branch