Exoscale cloud provider support?

Hi! I was wondering if there's any support for [Exoscale](https://www.exoscale.com/) in PerfKitBenchmarker? I noticed there's support for AWS, Azure, GCP, and even CloudStack, but I couldn't find anything for Exoscale.

This seems like it could be a relatively straightforward addition since:

PKB already has CloudStack support, and Exoscale was historically CloudStack-based (though they've moved to their own API v2)
Exoscale's driver in Apache Libcloud is actually based on the CloudStack driver
They offer S3-compatible storage and compute instances similar to other supported providers

If there isn't support yet, could someone point me in the right direction for implementing it? I'd be interested in contributing this if it's something the project would accept.

Thanks!

Start by reading PerfKitBenchmarker’s existing CloudStack support and Apache Libcloud’s Exoscale driver, then compare the provider patterns used for AWS, Azure, and GCP. Define what Exoscale compute and S3-compatible storage support must cover; done means the provider is integrated sufficiently for the relevant benchmarks and its behavior is verified.

Written by the indexing model from the issue text.