Create Pinta compilation Dockerfile for Ubuntu-focal

[Stdedos]

Continuing from https://bugs.launchpad.net/bugs/1786822, I am trying to build a Dockerfile, that will "build the deb package for Pinta".

As you have no `debian/` directory (which is necessary in order to build packages, e.g. https://salsa.debian.org/ribalda/ugrep/-/tree/debian/debian), I am instead finishing my task right now to `RUN dotnet publish -c release -o /app --no-restore` (and then hopefully it already builds a debian package, or I'll ask/you'll provide more information on how did the packaging went "back in the days")

However, at this point, I am getting:

```
Step 14/16 : RUN ./autogen.sh
 ---> Running in 0c9cc3b99458
Running intltoolize
I am going to run ./configure with no arguments - if you wish
to pass any to it, please specify them on the ./autogen.sh command line.
Running aclocal -I . ...
Running automake --gnu ...
configure.ac:32: installing './compile'
configure.ac:3: installing './install-sh'
configure.ac:3: installing './missing'
Running autoconf ...
Running ./configure ...
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /usr/bin/mkdir -p
checking for gawk... no
checking for mawk... mawk
checking whether make sets $(MAKE)... no
checking whether make supports nested variables... no
checking whether UID '0' is supported by ustar format... yes
checking whether GID '0' is supported by ustar format... yes
checking how to create a ustar tar archive... gnutar
checking for pkg-config... /usr/bin/pkg-config
checking pkg-config is at least version 0.20... yes
checking for dotnet... /usr/bin/dotnet
./configure: line 3109: syntax error near unexpected token `$DOTNET_VERSION,'
./configure: line 3109: `AX_COMPARE_VERSION($DOTNET_VERSION, ge, $DOTNET_MINIMUM_VERSION,'
The command '/bin/sh -c ./autogen.sh' returned a non-zero code: 2
```

and I am wondering, if you know what's wrong.

I am using the https://hub.docker.com/_/microsoft-dotnet-sdk from Microsoft, version 6.0-focal (since I am targeting focal i.e. my system initially)

[Stdedos (stdedos)]

*e.g. https://salsa.debian.org/ribalda/ugrep/

[Cameron White (cameronwhite91)]

Some googling suggests that the autoconf-archive package might need to also be installed?

Also, https://code.launchpad.net/~cameronwhite91/+junk/pinta-stable-packaging has the Debian packaging code that was being used for the pinta-stable PPA