[8.14](backport #39940) x-pack/filebeat/input/cel: fix handling of in…

…finite values in rates (#39986)

* x-pack/filebeat/input/cel: fix handling of infinite values in rates (#39940)

The protobuf.Value.AsInterface method encodes +Inf as "Infinity" so
ensure that we accept that string.

(cherry picked from commit 1f8ad02)

* remove irrelevant changelog entry

---------

Co-authored-by: Dan Kortschak <dan.kortschak@elastic.co>

CHANGELOG.next.asciidoc

@@ -140,6 +140,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - Add setup option `--force-enable-module-filesets`, that will act as if all filesets have been enabled in a module during setup. {issue}30915[30915] {pull}99999[99999]
 - Made Azure Blob Storage input GA and updated docs accordingly. {pull}37128[37128]
 - Made GCS input GA and updated docs accordingly. {pull}37127[37127]
+- Fix handling of infinite rate values in CEL rate limit handling logic. {pull}39940[39940]
 
 *Auditbeat*
 

x-pack/filebeat/input/cel/input.go

@@ -675,7 +675,7 @@ func getLimit(which string, rateLimit map[string]interface{}, log *logp.Logger)
 	case float64:
 		limit = rate.Limit(r)
 	case string:
-		if !strings.EqualFold(r, "inf") {
+		if !strings.EqualFold(strings.TrimPrefix(r, "+"), "inf") && !strings.EqualFold(strings.TrimPrefix(r, "+"), "infinity") {
 			log.Errorw("unexpected value returned for rate limit "+which, "value", r, "rate_limit", mapstr.M(rateLimit))
 			return limit, false
 		}