Make plugin support all Kopia Repository Types

[dougkirkley]

I am looking to make the switch from Crunchy Postgres to CloudNativePG. One of the setbacks currently is that we use S3 for backups currently and we can't use Barman due to its license. I looked at this repo as an example of how to implement an object store plugin for backups to see how feasible that would be and saw that Kopia has many different repository types that could be used to support many different types of backups. Is there a way we can make this plugin more generic to allow more repository options and their flags? I had to copy a lot of reusable code in this repo to have a working example for s3 backups. Thanks