The `ignore_malformed` option is supported by a few of our field types, mainly numerics and dates, to still accept the document when such fields hold malformed values. See https://www.elastic.co/guide/en/elasticsearch/reference/current/ignore-malformed.html. Also `ignore_malformed` is an index level setting that gets applied to all field types that support it. 

The boolean field type does not support `ignore_malformed` but it should, so that if a boolean field cannot be parsed as a boolean, the document can still be accepted.


server/src/main/java/org/elasticsearch/index/mapper/BooleanFieldMapper.java
private final Boolean nullValue;
        private final FieldValues<Boolean> scriptValues;
        public BooleanFieldType(
            String name,
            boolean isIndexed,
            boolean isStored,
            boolean hasDocValues,
            Boolean nullValue,
            FieldValues<Boolean> scriptValues,
            Map<String, String> meta
        ) {
            super(name, isIndexed, isStored, hasDocValues, TextSearchInfo.SIMPLE_MATCH_ONLY, meta);
            this.nullValue = nullValue;
            this.scriptValues = scriptValues;
        }
        public BooleanFieldType(String name) {
            this(name, true);
        }
        public BooleanFieldType(String name, boolean isIndexed) {