build(deps): bump github.com/gophercloud/gophercloud

Bumps [github.com/gophercloud/gophercloud](https://github.com/gophercloud/gophercloud) from 0.11.0 to 0.20.0.
- [Release notes](https://github.com/gophercloud/gophercloud/releases)
- [Changelog](https://github.com/gophercloud/gophercloud/blob/master/CHANGELOG.md)
- [Commits](https://github.com/gophercloud/gophercloud/compare/v0.11.0...v0.20.0)

---
updated-dependencies:
- dependency-name: github.com/gophercloud/gophercloud
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

vendor/github.com/gophercloud/gophercloud/README.md

@@ -60,6 +60,13 @@ prompted for your password.
 
 ### Authentication
 
+> NOTE: It is now recommended to use the `clientconfig` package found at
+> https://github.com/gophercloud/utils/tree/master/openstack/clientconfig
+> for all authentication purposes.
+>
+> The below documentation is still relevant. clientconfig simply implements
+> the below and presents it in an easier and more flexible way.
+
 Once you have access to your credentials, you can begin plugging them into
 Gophercloud. The next step is authentication, and this is handled by a base
 "Provider" struct. To get one, you can either pass in your credentials