Add a speakup module

**Is your feature request related to a problem? Please describe.**

Hardware synths cannot be used in Orca

**Describe the solution you'd like**

Adding a module to speech-dispatcher that emits text to /dev/synth would let orca access speakup-driven hardware synthesizers.

**Additional context**

requested on
https://www.freelists.org/post/orca/Can-Orca-work-with-hardware-synthesizers

Start by reviewing the speech-dispatcher module interfaces and the requested /dev/synth integration. Check how Orca would access a module that emits text to /dev/synth, and define done as hardware synthesizers becoming usable through Orca; the issue does not identify specific files or tests.

Written by the indexing model from the issue text.