Make "noop" request breaker a non-dynamic setting

The issue with making it dynamic is that in the event a cluster is
switched from a noop to a concrete implementation, there may be
in-flight requests, once these requests complete we adjust the breaker
with a negative number and trip an assertion.

This also rarely uses noop breakers in InternalTestCluster
Update cluster.asciidoc

Fixed asciidoc syntax
Update update-settings.asciidoc

Removed deprecated `cluster.routing.allocation.disable` settings
Stats : Add time in index throttle to stats.

This commit adds the time spent throttling indexing to a single thread to the stats API.

Closes #7861
Stats : Add time spent in index throttle.

Changes after review. Now track the time actually throttle locked rather than when we could be throttle locked.
Also add test that failed to make it in to last commit.
[TEST] Fix throttle test to always sleep for correct amount of time.
Stats : Add time in index throttle

This commit adds throttle stats to the indexing stats and uses a call back from InternalEngine to manage the stats.
Also includes updates the IndexStatsTests to test for these new stats.
Stats added :
```
throttle_time_in_millis
is_throttled
```

See #7861