#12657

Merge 2.9 with these PRs:

#12566 Make `coreos/go-systemd' buildable on windows
#12594 [Charmhub] - `Juju info` updates based on upcoming api changes.
#12596 Pebble support with *-workload-ready hook.
#12602 Static analysis checks
#12604 [2.9] Do not attempt to set proxy settings for windows/centos workloads
#12605 [2.9] Use positional arguments for azure clients
#12607 Clean up model migration code
#12608 Allow bundle to update existing offers
#12609 EC2 fix panic
#12614 Errcheck linter fixes
#12615 Allow bundle to update existing offers
#12617 Fixes permission for model operator.
#12619 Add set-series integration test
#12620 Fix asserts used when finalising an action
#12621 Relocates DNS and resolve.conf parsing from network to core/network
#12622 Move NetworkConfigSource from api/common to core/network
#12623 Indirection for network config sourced addresses
#12627 Ensure relation units
#12629 Record why a cloud credential gets marked invalid and expose via show-model, status
#12630 Fix double upgraded
#12633 Update how channel is created in ApplicationsInfo.
#12634 Fix uniter loop when a relation is removed out of bandge case.
#12637 Improve maas cli output handling in acceptance tests
#12638 Bundle export with channel
#12641 Bundle diff output with charm url names
#12643 Expose charm channel in juju status
#12644 Fix service type translation for k8s applications
#12647 Fix acceptance test bug in get_uptime
#12650 Ensure we normalize the charm url in bundle handler
#12651 Use python 3.6 compat fix for handling maas cli output
#12652 Use python 3.6 compatible way to capture subprocess stdout/err output
#12653 missing container status of creating
#12654 Move 2.8.10 upgrade step to 2.8.9


```
# Conflicts:
# api/backups/restore.go
# apiserver/facades/client/backups/restore.go
# caas/kubernetes/provider/operator.go
# cloudconfig/podcfg/image.go
# cmd/containeragent/main_nix.go
# cmd/containeragent/main_test.go
# cmd/containeragent/unit/agent.go
# cmd/containeragent/unit/agent_test.go
# cmd/juju/action/run.go
# cmd/juju/action/showoutput.go
# cmd/juju/commands/exec.go
# cmd/juju/commands/exec_test.go
# go.mod
# go.sum
# juju/testing/conn.go
# state/action_test.go
# state/applicationoffers.go
# state/backups/files.go
# state/backups/restore_test.go
# state/upgrades.go
# worker/machineactions/worker.go
# worker/restorewatcher/manifold.go
# worker/restorewatcher/worker.go
# worker/uniter/runner/jujuc/mocks/context_relation_mock.go
# worker/uniter/util_test.go
```

## QA steps

See PRs