Upgrade Polly strategies to V8 API

[SondreJDigdir]

Polly's made larger changes to their API in their SDK from version 7 to 8. Upgrading to V8 doesn't immediately require any changes, however how some policies are configured should be updated to be done the V8-way.

Polly has a migration guide from 7 to 8: https://www.pollydocs.org/migration-v8.html

I don't think this is urgent, however it should be done sooner rather than later as I would presume that when they go to V9 they won't support v7 methods anymore.

[SondreJDigdir]

Currently no equivalent built in support for the cacheasync policies that we use in Dan.Common and Dan.Core. Doesn't seem like we'll get immediate support App-vNext/Polly#1127, so we need to decide when we want to change to using resilience strategies and if we want to make our own cache strategy or look for some other packages.