Use matrix_bot_chatgpt_context for CHATGPT_CONTEXT

Set OPEN_AI to matrix_bot_chatgpt_openai_pro

This container needs a writable $HOME, and will fail at startup if
there isn't one.

Provide one by pointing HOME to a path under the mounted /data
directory.

Co-Authored-By: Slavi Pantaleev <slavi@devture.com>