fix: notify users when wrong coqpit package is installed

[eginhard]

coqui-tts 0.25.0 switched to the forked coqpit-config package. When users update to that version, they will likely still have the original, now incompatible coqpit package in their environment. This PR adds a helpful error message in that case:

from TTS.api import TTS
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "TTS/__init__.py", line 14, in <module>
    raise ImportError(msg)
ImportError: coqui-tts uses a forked version of coqpit, but you still have the original package installed. Run the following to avoid conflicts:
  pip uninstall coqpit
  pip install coqpit-config

Fixes #274