Remove superflous parameter `overseer_enable_anyways` and make parachain node type more explicit (#7617)

* Remove superflous parameter `overseer_enable_anyways`

We don't need this flag, as we don't need the overseer enabled when the
node isn't a collator or validator.

* Rename `IsCollator` to `IsParachainNode`

`IsParachainNode` is more expressive and also encapsulates the state of
the parachain node being a full node. Some functionality like the
overseer needs to run always when the node runs alongside a parachain
node. The parachain node needs the overseer to e.g. recover PoVs. Other
things like candidate validation or pvf checking are only required for
when the node is running as validator.

* FMT

* Fix CI