Revert grammar endpoint doc example to clean JSON format

Signed-off-by: Eric Wei <mengwei.eric@gmail.com>

Author: mengweieric

docs/user/ppl/interfaces/endpoint.md

@@ -302,16 +302,26 @@ You can send an HTTP GET request to endpoint **/_plugins/_ppl/_grammar** to fetc
 
 ### Example
 
-```bash
-curl -sS -X GET localhost:9200/_plugins/_ppl/_grammar | python3 -m json.tool | grep -E '"bundleVersion"|"antlrVersion"|"startRuleIndex"|"ignoredTokens"|"rulesToVisit"'
+```bash ppl ignore
+curl -sS -X GET localhost:9200/_plugins/_ppl/_grammar
 ```
 
 Expected output (trimmed):
 
-```text
-"bundleVersion": "1.0",
-"antlrVersion": "4.13.2",
-"startRuleIndex": 0,
-"ignoredTokens": [
-"rulesToVisit": [
+```json
+{
+  "bundleVersion": "1.0",
+  "antlrVersion": "4.13.2",
+  "grammarHash": "sha256:...",
+  "startRuleIndex": 0,
+  "lexerSerializedATN": [4, ...],
+  "parserSerializedATN": [4, ...],
+  "lexerRuleNames": ["SEARCH", "..."],
+  "parserRuleNames": ["root", "..."],
+  "literalNames": [null, "'SEARCH'", "..."],
+  "symbolicNames": [null, "SEARCH", "..."],
+  "tokenDictionary": {"PIPE": 196, "...": 0},
+  "ignoredTokens": [472, 473, "..."],
+  "rulesToVisit": [200, 201, "..."]
+}
 ```