Allow Netherite provider to be implemented separately

[sebastianburckhardt]

Support for using the EventSourced backend, as in the work-in-progress PR Azure/durabletask#461.

Besides adding a durability provider, the changes include:

• turn off message sorter logic for backend that delivers messages in order
• support poll-free version of WaitForOrchestration for backends that support client responses
• change tracing options for unit tests

[davidmrdavid]

@sebastianburckhardt , if this is WIP, should we consider making it a draft PR? :)

[sebastianburckhardt]

Not sure what the difference is between draft and WIP?

Since we just decided to restructure the projects I can't be quite sure what will change. Currently figuring this out. My guess is that in its eventual form, this PR will stay similar, as far as modifications to existing files are concerned, but it will not include the new durability provider.

[davidmrdavid]

@sebastianburckhardt , a draft is a GitHub UI feature to acknowledge that a PR is work-in-progress. I've used it in the past to make a clean separation between PRs that need immediate reviews for immediate merge consideration and the PRs that do not. You can read about it here:
https://github.blog/2019-02-14-introducing-draft-pull-requests/

Essentially if you CTRL+F "draft" in this page, you should be able to convert this into a draft PR. Just a suggestion! I can also do it for you if you'd like

[sebastianburckhardt]

This is now ready to be reviewed. It only contains the changes needed for implementing Netherite as an external NuGet package. The changes include:

• turn off message sorter logic for backend that delivers messages in order
• support poll-free version of WaitForOrchestration for backends that support client responses
• add three protected methods to DurabilityProvider that allow implementations to access functionality that is otherwise internal

[davidmrdavid]

Looks pretty good to me, I give it my thumbs-up but I do have suggestions for improvements, please see my comments.

I'll wait for a second pair of eyes to give this the approval 😄

[davidmrdavid]

Ah it also seems like there's a merge conflict with src/WebJobs.Extensions.DurableTask/DurableTaskExtension.cs

[davidmrdavid]

Really happy with the latest changes. LGTM! Still waiting on a 2nd pair of eyes just in case

[davidmrdavid]

Re-started the CI build checks since it appears to have been running for over an hour and thus timed-out. Sometimes this happens, for some reason, with the CI. Hoping they pass now!

[ConnorMcMahon]

Overall looks fairly good, just a few questions.

[ConnorMcMahon]

LGTM!