Add Ingest-Processor specific Rest Endpoints & Add Grok endpoint (#25059)

This PR enables Ingest plugins to leverage processor-scoped REST
endpoints. First of which being the Grok endpoint that retrieves
Grok Patterns for users to retrieve all the built-in patterns.
Example usage: Kibana Grok Autocomplete!

1 files changed, 26 insertions, 0 deletions

diff --git a/docs/reference/ingest/ingest-node.asciidoc b/docs/reference/ingest/ingest-node.asciidoc
index 076545cdd2..4c96ee9c6d 100644
--- a/docs/reference/ingest/ingest-node.asciidoc
+++ b/docs/reference/ingest/ingest-node.asciidoc
@@ -1454,6 +1454,32 @@ second (index starts at zero) pattern in `patterns` to match.
 This trace metadata enables debugging which of the patterns matched. This information is stored in the ingest
 metadata and will not be indexed.
 
+[[grok-processor-rest-get]]
+==== Retrieving patterns from REST endpoint
+
+The Grok Processor comes packaged with its own REST endpoint for retrieving which patterns the processor is packaged with.
+
+[source,js]
+--------------------------------------------------
+GET _ingest/processor/grok
+--------------------------------------------------
+// CONSOLE
+
+The above request will return a response body containing a key-value representation of the built-in patterns dictionary.
+
+[source,js]
+--------------------------------------------------
+{
+  "patterns" : {
+    "BACULA_CAPACITY" : "%{INT}{1,3}(,%{INT}{3})*",
+    "PATH" : "(?:%{UNIXPATH}|%{WINPATH})",
+    ...
+}
+--------------------------------------------------
+// NOTCONSOLE
+
+This can be useful to reference as the built-in patterns change across versions.
+
 [[gsub-processor]]
 === Gsub Processor
 Converts a string field by applying a regular expression and a replacement.