Consistent naming for the Genesis/Devoted BlockFetch decision logic

In the Genesis documentation (added in #1174),

> ### The Devoted BlockFetch Component
>
> > Note that in the code, this component is still called *BulkSync BlockFetch* at the moment.

The goal is to use a consistent name, e.g. by changing the [implementation](https://github.com/IntersectMBO/ouroboros-network/blob/28b731cde005a1de0b4be0ea0bd16852e827c1bc/ouroboros-network/src/Ouroboros/Network/BlockFetch/Decision/Genesis.hs), either the module names or just in e.g. the Haddocks.

Start with the implementation linked in the issue, ouroboros-network/src/Ouroboros/Network/BlockFetch/Decision/Genesis.hs, and compare its terminology with the Genesis documentation. Choose a consistent Devoted BlockFetch name, then update the relevant module names or Haddocks and confirm that the documentation and implementation use the same terminology.

Written by the indexing model from the issue text.