Replace mimic3 with piper

[texhnolyze]

Summary

As stated in https://github.com/bit-bots/ansible/pull/14 and #529, the mimic3 company mycroft is defunct and does not supply updates to the tts system anymore, and we even had to adjust some code to use different URLs for downloads.

Describe the solution you'd like

Replace setup and usage of mimic3 with piper in bitbots_tts, anisble and requirements/robot.txt.

Describe alternatives you've considered

Alternatively, we could look at other available tts systems.