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/test/java/org/elasticsearch/index/mapper/BooleanScriptFieldTypeTests.java
"*",
                    simpleMappedFieldType().existsQuery(mockContext()),
                    ootb.fieldType().existsQuery(mockContext())
                );
                boolean term = randomBoolean();
                assertSameCount(
                    searcher,
                    source,
                    term,
                    simpleMappedFieldType().termQuery(term, mockContext()),
                    ootb.fieldType().termQuery(term, mockContext())
                );
                List<Boolean> terms = randomList(0, 3, ESTestCase::randomBoolean);
                assertSameCount(
                    searcher,
                    source,
                    terms,
                    simpleMappedFieldType().termsQuery(terms, mockContext()),
                    ootb.fieldType().termsQuery(terms, mockContext())
                );
                boolean low;
                boolean high;
                if (randomBoolean()) {
                    low = high = randomBoolean();
                } else {
                    low = false;
                    high = true;
                }
                boolean includeLow = randomBoolean();
                boolean includeHigh = randomBoolean();