DEV: Improve support for Ubuntu 20 and Debian 12

[Arkshine]

I've been looking to improve the guide to setting up a development environment and tested the different versions of Ubuntu and Debian (fresh dev installation on cloud hosting)

What does this PR is to fix Ubuntu 20 and Debian 12 installations.
Ubuntu 20 is still officially supported.

In short:

• Removed the Debian backports usage. The libheif and libaom libraries are not backported.
• libwebp7 is required in Debian 12.

Debian 10 and Ubuntu 18 are voluntarily ignored in the changes because they are either no longer supported or too old.

Debian

There is no backports installed by default.
E.g. Debian 11:

E: The value 'bullseye-backports' is invalid for APT::Default-Release as such a release is not available in the sources
failed

Looking at the Debian backports:

• Debian 11 Bullseye https://backports.debian.org/bullseye-backports/overview/
• Debian 12 Bookworm: https://backports.debian.org/bookworm-backports/overview/

The libraries are not backported. I don't see any reason to try to use them.

10

The script fails on ImageMagick. The required version doesn't match.

checking for libheif >= 1.4.0... no

# apt show libheif1
Package: libheif1
Version: 1.3.2-2~deb10u1

It's possible to compile from source.
This distribution is fairly old, and It seems to be a good idea to use at least the same version as Discourse (Debian 11)

11

With the change introduced in this PR, it works great.
Discourse uses the bullseyes-slim docker image, and the bullseye-backports is included by default.

12

# cat /etc/issue
Debian GNU/Linux 12 \n \l

With the change introduced in this PR, it works great.

Ubuntu

18

Similar to Debian 10, this can work with some effort. However, the distribution is fairly old and unsupported.
To make it work, you need at least Node 16 and libeom/heif compiled from the source.
We can skip it.

20

With the change introduced in this PR, it works great.

22

It works great as it is.

[Arkshine]

I made an update. I tested Debian 10, 11, and 12, and this PR improves support for Ubuntu 20 and now Debian 12.
The first message should be more descriptive.

EDIT: sorry for the unnecessary noise, I wanted to rename the branch.

[Arkshine]

The build failure doesn't seem related to this PR. 🤔 It errors with:

#10 5.898 Couldn't connect to Redis
#10 5.930 rake aborted!
#10 5.930 Redis::CannotConnectError: Error connecting to Redis on localhost:6379 (Errno::EADDRNOTAVAIL) (Redis::CannotConnectError)