apt-based install commands only work on LTS

https://www.edgedb.com/install#linux-debianubuntults contains instructions for installing on Linux using a package manager.

The command to configure the apt sources is shown here:
`
echo deb [signed-by=/usr/local/share/keyrings/edgedb-keyring.gpg]\
https://packages.edgedb.com/apt \
$(grep "VERSION_CODENAME=" /etc/os-release | cut -d= -f2) main \
| sudo tee /etc/apt/sources.list.d/edgedb.list
`
From ensuing [discussion in slack](https://edgedb.slack.com/archives/CNECHA9EW/p1689806641192179) it became clear that this command only works on an LTS release of ubuntu. It is not exactly clear what the fix is. Some suggestions are:

1. Document before the command that it will only work on LTS.
2. Do not get the version codename from /etc/os-release - either ask the user or hard-code the latest that will work which at his time is jammy. Because this is a documnted command on the web site, it could be updated when there is a new supported LTS.
3. Include in the documented commands a [menu to select](https://linuxize.com/post/bash-select/) the release from a list of supported releases. The documentation can be updated when there is a new release.

Start at the Linux Debian/Ubuntu LTS install instructions at https://www.edgedb.com/install#linux-debianubuntults and inspect the apt-source command shown there. Review the linked Slack discussion to understand the reported LTS limitation, then determine the agreed documentation change and verify that the resulting instructions identify supported releases accurately.

Written by the indexing model from the issue text.