[SPEC] Renamed benchmark endpoints

benchmark.submit -> benchmark
benchmark.list   -> list_benchmarks
benchmark.abort  -> abort_benchmark

And fixed the related tests
[SPEC] Added missing list_benchmarks test
[SPEC] The scroll_id is no longer a required qs param
Can be passed in the body instead
[DOCS] getting started tutorial
[SPEC] Added path without scroll_id to clear_scroll
Change default merge throttling to 50MB / sec

The current setting of 20MB/sec seems to be too conservative given
the capabilities of modern hardware. Even on cloud infrastructure this
seems to be too lowish. A 50MB default should provide better out of the box
performance
Disable benchmark tests until nodes set to run with
-Des.node.bench=true
Re-order log statements to be correct for segment and top level warming.