Remove usage of JobStorage.Current

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When using the ASP.NET Core Hangfire integration, i.e. services.AddHangfire(...) the JobStorage.Current static property may never be assigned through the application lifetime as it's injected.

We can get rid of JobStorage.Current and access the storage from either the new IBackgroundJobClientV2 interface introduced in Hangfire 1.8 (Atom + Trigger classes) or through the ApplyStateContext (AtomDeletedStateElectionFilter class).

Note that I have opened this pull request as a draft since it depends on Hangfire 1.8.0-rc2 which is not yet the final 1.8 version.

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Note: this pull request will be really useful when https://github.com/HangfireIO/Hangfire/pull/2146 will also be merged.

[ahydrax]

Got it, ping me when it's ready

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Now that Hangfire 1.8 is released it might be worth considering.