juju#10363

## Description of change

2.5 accepted error forming without a formatting directive but 2.6 insists on it. Backporting to keep codebase in sync.

…e-username

juju#10369

## Description of change

Not all user store operations correctly formatted the mongo document id.
This fixes the behaviour in all affected user state functions and add tests to ensure this behaviour works.

Previously `juju register` with a secret token failed because the update password didn't behave correctly when a username contained uppercase.

## QA steps

Adding a user and registering that user should succeed when the username contains uppercase.
```
juju bootstrap localhost
juju add-user TestName
XDG_DATA_HOME=`mktemp -d` juju register <secret token from add-user>`
```

## Documentation changes

N/A

## Bug reference

[https://bugs.launchpad.net/juju/+bug/1833449](https://bugs.launchpad.net/juju/+bug/1833449)

juju#10355

Juju 2.5 changed the default [Azure Load Balancer SKU](https://docs.microsoft.com/en-us/azure/load-balancer/load-balancer-overview#skus) from Basic to Standard. Unfortunately, models created by Juju 2.4 get stuck when their controllers are upgraded.

This change introduces a model config parameter `load-balancer-sku-name` (name chosen to be consistent with the Azure SDK naming scheme) that allows for operators to select between Basic and Standard types. It also cleans up some of the internals of the Azure provider, which should make it friendlier to newcomers to the code.

## QA steps
```
snap install juju # (if required)
snap switch juju channel=2.4/stable
/snap/juju/current/bin/juju bootstrap azure c-az
/snap/juju/current/bin/juju deploy ubuntu
```

(Assuming `juju` is this branch)

```
juju upgrade-model -m controller --build-agent
```
>```
> no prepackaged agent binaries available, using local agent binary 2.5.8.1 (built from source)
> best version:
> 2.5.8.1
> started upgrade to 2.5.8.1
>```

```
juju model-config -m controller load-balancer-sku-name=Basic
juju add-unit ubuntu
```


## Documentation changes

Required. We need to document the new model config parameter.

## Bug reference

* https://bugs.launchpad.net/juju/+bug/1824465

juju#10374

## Description of change

As per linked bug, when a user specified cloud as well as the region to which to bootstrap, Juju supplies unhelpful message about credentials rather than warning about invalid region.

This PR validates that a user supplied region is valid for a given cloud.

## QA steps

At bootstrap command, specify an invalid region for your desired cloud.
For example:
```
$ juju bootstrap aws/eu-west mycontroller 
Available cloud regions are ap-northeast-1, ap-northeast-2, ap-south-1, ap-southeast-1, ap-southeast-2, ca-central-1, eu-central-1, eu-west-1, eu-west-2, eu-west-3, sa-east-1, us-east-1, us-east-2, us-west-1, us-west-2
ERROR region "eu-west" for cloud "aws" not valid
```
## Bug reference

https://bugs.launchpad.nacet/juju/+bug/1632735

juju#10375

Bring forward:
juju#10355 
juju#10363