* Add ingest info to Cluster Stats (#48485)
This commit enhances the ClusterStatsNodes response to include global
processor usage stats on a per-processor basis.
example output:
```
...
"processor_stats": {
"gsub": {
"count": 0,
"failed": 0
"current": 0
"time_in_millis": 0
},
"script": {
"count": 0,
"failed": 0
"current": 0,
"time_in_millis": 0
}
}
...
```
The purpose for this enhancement is to make it easier to collect stats on how specific processors are being used across the cluster beyond the current per-node usage statistics that currently exist in node stats.
Closes#46146.
* fix BWC of ingest stats
The introduction of processor types into IngestStats had a bug.
It was set to `null` and set as the key to the map. This would
throw a NPE. This commit resolves this by setting all the processor
types from previous versions that are not serializing it out to
`_NOT_AVAILABLE`.
4be54402de