* flatpak: improve flatpak name parsing in `_parse_flatpak_name`
* changelog: add changelog fragment
* flatpak: fix condition in `_is_flatpak_id` function
* chore: update changelog fragment
* docs(flatpak): add guidelines for application IDs in comments
Fixes#6563 by extending the allowed values of the `state` parameter to
include `latest`. To do this, the `update_flat()` function is introduced
which borrows the majority of its implementation from both the existing
`install_flat()` and `remove_flat()` functions. The documentation and
examples have been expanded describing what to expect when using
`state=latest`.
Alexei Znamensky
Járedy Alves
Kenneth Benzie (Benie)
Felix Fontein
Svenum
Brian Coca