Previously run values was using interface{} and casting to provide
execution options for tests. Making function generic reduces boilerplate
code needed to setup and use test parameters.

Epic: none

Release note: None

Previously each rangefeed processor run a dedicated goroutine to
process range events. With high replica density that produced
10K's of goroutines waking up periodically and overloading go
scheduler.
This commit adds a version of processor that uses a scheduler
with a fixed pool of workers to process all ranges on the node.
Scheduler based processor is off by default and can be enabled
by using `kv.rangefeed.scheduler.enabled` cluster setting.
Number of workers in scheduler pool is determined by environment
variable `COCKROACH_RANGEFEED_SCHEDULER_WORKERS`.

Epic: none

Release note (performance improvement): Added scheduler based
rangefeed processor which improves rangefeed and changefeed
performance for very large tables. New processor is disabled by
default, but can be enabled via `kv.rangefeed.scheduler.enabled`
cluster setting.

This commit adds slow transaction pusher to scheduler based rangefeed.
Store will trigger bulk enqueueing of relevant push events to
eligible processors.

Epic: none

Release note: None