Rebase to Ubuntu 22.04

Rebase charm to Ubuntu 22.04 to resolve build issues on 20.04
and reduce requirements management complexity.

Change-Id: Ia96db646c27f37d83cc11bf79ebb4711f9a48cfc

charms/horizon-k8s/charmcraft.yaml

@@ -2,10 +2,10 @@ type: "charm"
 bases:
   - build-on:
     - name: "ubuntu"
-      channel: "20.04"
+      channel: "22.04"
     run-on:
     - name: "ubuntu"
-      channel: "20.04"
+      channel: "22.04"
 parts:
   update-certificates:
     plugin: nil
@@ -20,6 +20,5 @@ parts:
       - git
       - libffi-dev
       - libssl-dev
-    charm-python-packages:
-      - setuptools < 58
-      - cryptography < 3.4
+      - rustc
+      - cargo

charms/horizon-k8s/requirements.txt

@@ -4,24 +4,10 @@
 #     https://github.com/openstack-charmers/release-tools
 #
 
-# NOTE: newer versions of cryptography require a Rust compiler to build,
-# see
-# * https://github.com/openstack-charmers/zaza/issues/421
-# * https://mail.python.org/pipermail/cryptography-dev/2021-January/001003.html
-#
-cryptography<3.4
+cryptography
 jinja2
 jsonschema
 lightkube
 lightkube-models
 ops
 git+https://opendev.org/openstack/charm-ops-sunbeam#egg=ops_sunbeam
-
-# python-keystoneclient  # keystone-k8s
-
-# git+https://opendev.org/openstack/charm-ops-interface-tls-certificates#egg=interface_tls_certificates
-
-# Note: Required for cinder-k8s, cinder-ceph-k8s, glance-k8s, nova-k8s
-# git+https://opendev.org/openstack/charm-ops-interface-ceph-client#egg=interface_ceph_client
-# Charmhelpers is only present as interface_ceph_client uses it.
-# git+https://github.com/juju/charm-helpers.git#egg=charmhelpers