Drop Ubuntu 18.04, 20.04 and 22.04 support

[joachimmetz]

Various dependencies on Ubuntu 18.04, 20.04 and 22.04 lagging behind making maintenance time consuming. Drop Ubuntu 18.04, 20.04 and 22.04 support

• No support for pyproject.toml files
• Ubuntu 18.04 ships with Python 3.6 and that is blocking Python types adoption
• Ubuntu 20.04 ships with old gettext that is blocking libyal moving to a new version
• Ubuntu 22.04 ships with old version of setuptools

autopoint: *** The AM_GNU_GETTEXT_VERSION declaration in your configure.ac
               file requires the infrastructure from gettext-0.21 but this version
               is older. Please upgrade to gettext-0.21 or newer.

• Ubuntu 18.04 remove from testing
• Ubuntu 18.04 remove from dev
• Ubuntu 18.04 remove from staging
• Ubuntu 18.04 remove from stable
• Ubuntu 20.04 remove from testing
• Ubuntu 20.04 remove from dev
• Ubuntu 20.04 remove from staging
• Ubuntu 20.04 remove from stable
• Ubuntu 22.04 remove from testing
• Ubuntu 22.04 remove from dev
• Ubuntu 22.04 remove from staging
• Ubuntu 22.04 remove from stable

[joachimmetz]

Ubuntu 18.04 builds removed from testing, dev and staging

[joachimmetz]

Ubuntu 20.04 builds removed from testing,

[joachimmetz]

Ubuntu 20.04 builds removed from dev and staging.