1.13.5-dev10

istio: add metric for debouncing (#40523)

* istio: add metric for debouncing

This CL adds metric for the delay between a first config change
enters deboucing until the final merged push request is pushed into
the push queue. This time plus the proxy convergence time give us
an upper bound on the total delay between a config change and the
change is pushed to proxies.

Also increased the buckets since logging shows that the debounce time
is pretty long (more than 1 minute).

Change-Id: I3220f9c3188824ea6925151ff6837f91aac5a15a
Reviewed-on: https://gerrit.musta.ch/c/public/istio/+/3512
Reviewed-by: Weibo He <[email protected]>
Reviewed-by: Ryan Smick <[email protected]>
Reviewed-by: Jungho Ahn <[email protected]>

* istio: fix debounceTime typo

Change-Id: I9977c597768360cc3dd485dbf21bd9afdb2f5151
Reviewed-on: https://gerrit.musta.ch/c/public/istio/+/3517
Reviewed-by: Weibo He <[email protected]>

* istio: handle debounce time entirely in the debounce() function

To address comments in https://github.com/istio/istio/pull/40523,
we will record after push finishes inside the debounce function.
We can actually remove the DebounceStart field in the push context
as a result.

Also change the buckets as discussed in the PR.

Change-Id: I3b7a7860590e7e5ed4f13282b4398527de089c81
Reviewed-on: https://gerrit.musta.ch/c/public/istio/+/3519
Reviewed-by: Jungho Ahn <[email protected]>
Reviewed-by: Weibo He <[email protected]>