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 Parameter<Boolean> docValues = Parameter.docValuesParam(m -> toType(m).hasDocValues, true);
        private final Parameter<Boolean> indexed = Parameter.indexParam(m -> toType(m).indexed, true);
        private final Parameter<Boolean> stored = Parameter.storeParam(m -> toType(m).stored, false);
        private final Parameter<Boolean> nullValue = new Parameter<>(
            "null_value",
            false,
            () -> null,
            (n, c, o) -> o == null ? null : XContentMapValues.nodeBooleanValue(o),
            m -> toType(m).nullValue,
            XContentBuilder::field,
            Objects::toString
        ).acceptsNull();
        private final Parameter<Script> script = Parameter.scriptParam(m -> toType(m).script);
        private final Parameter<OnScriptError> onScriptError = Parameter.onScriptErrorParam(m -> toType(m).onScriptError, script);
        private final Parameter<Map<String, String>> meta = Parameter.metaParam();
        private final ScriptCompiler scriptCompiler;
        private final Version indexCreatedVersion;
        public Builder(String name, ScriptCompiler scriptCompiler, Version indexCreatedVersion) {
            super(name);
            this.scriptCompiler = Objects.requireNonNull(scriptCompiler);
            this.indexCreatedVersion = Objects.requireNonNull(indexCreatedVersion);
            this.script.precludesParameters(nullValue);
            addScriptValidation(script, indexed, docValues);
        }
        @Override
        protected Parameter<?>[] getParameters() {
            return new Parameter<?>[] { meta, docValues, indexed, nullValue, stored, script, onScriptError };
        }
        @Override