Use matrix_bot_chatgpt_context for CHATGPT_CONTEXT

matrix_bot_chatgpt_context=thread

This helps large deployments which need to open up thousands of ports
(matrix_coturn_turn_udp_min_port, matrix_coturn_turn_udp_min_port)

On a test VM, opening 1k ports takes 17 seconds for Docker to "publish"
all of these ports (setting up forwarding rules with the firewall, etc),
so service startup and shutdown take a long amount of time.

If host-networking is used, there's no need to open any ports at all
and startup/shutdown can be quick.

Inspired by: https://www.rtcsec.com/article/cve-2020-26262-bypass-of-coturns-access-control-protection/

Part of a security hardening provoked by:
https://www.rtcsec.com/article/cve-2020-26262-bypass-of-coturns-access-control-protection/

Set OPEN_AI to matrix_bot_chatgpt_openai_pro

Add support for OPENAI_PRO for ChatGPT pro subscriptions.

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.

Related to https://github.com/matrix-org/synapse/commit/3479599387164aca2613e88d169719

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2392

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