sotw: Ordered ADS mode

[alecholmez]

introduce optional resource ordering for guaranteed eventual consistency in ADS mode. closes #526

[alecholmez]

This PR branches off the work found here: https://github.com/envoyproxy/go-control-plane/pull/461 and brings it up to speed with the current state of go-control-plane. Credit to the original algorithm author @fxposter (would be great if he could review)/ We've found quite a few resource ordering issues in upstream xDS conformance test suites and this will hopefully provide a remedy to some of those problems.

I tried to introduce the change in a non intrusive way, if no opts are provided to the server everything will execute as before. If the new opt sotw.WithOrderedADS() is passed to a server, the resources will be in guaranteed ordering as in the prior art PR. This provides guaranteed eventual consistency which we did not have in the previous implementation but gives up some of the pressure relief from immediate response sending.

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[alecholmez]

Haven’t had much bandwidth to work this recently will get back to it soon.

[marcosrmendezthd]

any progress on this?

[alecholmez]

Need to fix the integration tests and then this should be ready for a rereview

[haoruolei]

Hi do we have updates on this PR?

[alecholmez]

This PR is ready! Hopefully we can merge soon

[alecholmez]

@valerian-roche tagging you on a review for this one

[haoruolei]

Hi is there any update on this?

[arkodg]

@alecholmez guessing a similar ordering enforcement will be required for delta + ads as well ?

[alecholmez]

@arkodg Yup we'll need to port this over