Update Docker container to v4

[SadieCat]

InspIRCd v4 will be out soon — inspircd/inspircd#2096.

Once it is out we should update the Docker container to v4.

I'm planning on waiting a month or so before doing this so we can iron out any issues allowing users to have a comfortable upgrade experience.

[SadieCat]

Reminder to myself to revert 513c33b (other than --raw-output) when I update the image to v4.

[SadieCat]

I'm probably going to update the container when v4.4 (the release after next) comes out.

[jacekjaros]

I'm probably going to update the container when v4.4 (the release after next) comes out.

can we assume then that docker image for v4 will be released in next few days then ;)

[SadieCat]

I'll get to it as soon as I can but it might take a while as (1) I'll need to rework a bunch of stuff because I'm not happy with how it works currently (2) I have a limited amount of free time lately.

[SadieCat]

I'm considering how to improve the Docker container for the v4 update and I'm thinking we should rework it so we have three images:

2. inspircd-slim (just the core modules and ssl_gnutls)
3. inspircd (every extra module we can legally ship enabled)
4. inspircd-contrib (based on inspircd, with every contrib module enabled)