[Feature Request] Install keyring by default or offer a way to install keyring without causing error messages

**Is your feature request related to a problem? Please describe.**

When calling `az devops login` for the very first time, it installs pythons keyring package. For some reason that's not included in the default setup. This adds needless time to a first invocation of `az devops login` on the GitHub Hosted Runners and Azure Pipelines.

You can force the installation of keyring using

```
echo "dummy" | az devops login
az devops logout
```

On the GitHub/Azure Pipelines hosted runner the provisioning of the image happens on a non-interactive session and `az devops login` fails with an error along those lines.

```
ERROR: (1312, 'CredRead', 'A specified logon session does not exist. It may already have been terminated')
```

Unfortunatly, `az devops` doesn't provide a clean way to install keyring during installation or through a command other than catching the failed login.

**Describe the solution you'd like**
Either azdevops should preinstall keyring during normal installation of the extension. It's unclear why it's not included in the first place.

Or there should be a clean way to run `az devops install-dependencies` or something to have it download its dependencies in a provisioning scenario.

I grabbed the following lines from the code:
```
$pythonPath = resolve-path (join-path ([System.IO.Path]::GetDirectoryName((Get-Command az).Path)) "..\python.exe")
Invoke-ValidateCommand -Command "& '$pythonPath' -m pip install keyring~=17.1.1 --target '$env:AZURE_EXTENSION_DIR\azure-devops' -vv --disable-pip-version-check --no-cache-dir"
```

and it works. But since there is no way to grab the correct version of keyring from anywhere other than the sourcecode of az devops, it's a very brittle contract.

For now we're looking into just swallowing any message printed by `az devops login`. But that's of course also a brittle contract.

```
cli.azext_devops.dev.common.pip_helper: installing keyring~=17.1.1
cli.azure.cli.core.extension.operations: Running: ['C:\\Program Files\\Microsoft SDKs\\Azure\\CLI2\\python.exe', '-m', 'pip', 'install', 'keyring~=17.1.1', '--target', 'C:\\Users\\WDAGUtilityAccount\\.azure\\cliextensions\\azure-devops', '-vv', '--disable-pip-version-check', '--no-cache-dir']
```

**Additional context**

I know I could also set an environment variable with an access token instead of calling `az devops login`, unfortunately that also adds a 10 second delay on the GitHub Hosted Runner / Azure Pipelines runner as it tries to run `az login`, sees it fail and only then reverts to using the token supplied on the commandline.