Fixed typo in documentation (#23406)

* Fixed typo in documentation

The option in "gap_policy" "insert_zeros" was missing a trailing "s"

* Update movavg-aggregation.asciidoc

Author: msancho

docs/reference/aggregations/pipeline/movavg-aggregation.asciidoc

@@ -27,7 +27,7 @@ A `moving_avg` aggregation looks like this in isolation:
         "buckets_path": "the_sum",
         "model": "holt",
         "window": 5,
-        "gap_policy": "insert_zero",
+        "gap_policy": "insert_zeros",
         "settings": {
             "alpha": 0.8
         }
@@ -40,7 +40,7 @@ A `moving_avg` aggregation looks like this in isolation:
 |Parameter Name |Description |Required |Default Value
 |`buckets_path` |Path to the metric of interest (see <<buckets-path-syntax, `buckets_path` Syntax>> for more details |Required |
 |`model` |The moving average weighting model that we wish to use |Optional |`simple`
-|`gap_policy` |Determines what should happen when a gap in the data is encountered. |Optional |`insert_zero`
+|`gap_policy` |Determines what should happen when a gap in the data is encountered. |Optional |`insert_zeros`
 |`window` |The size of window to "slide" across the histogram. |Optional |`5`
 |`minimize` |If the model should be algorithmically minimized.  See <<movavg-minimizer, Minimization>> for more
  details |Optional |`false` for most models