### Description

Dynamic mappings can greatly help the getting started experience but they currently don't apply to all types, one example is `dense_vector`.

It's been suggested to automatically map float arrays as dense vectors when there are more than 100 values, or a heuristic along these lines.
server/src/main/java/org/elasticsearch/index/mapper/DocumentParser.java
DocumentParsingObserver documentParsingObserver = source.toBeReported()
            ? documentParsingObserverSupplier.get()
            : DocumentParsingObserver.EMPTY_INSTANCE;
        try (
            XContentParser parser = documentParsingObserver.wrapParser(
                XContentHelper.createParser(parserConfiguration, source.source(), xContentType)
            )
        ) {
            context = new RootDocumentParserContext(mappingLookup, mappingParserContext, source, parser);
            validateStart(context.parser());
            MetadataFieldMapper[] metadataFieldsMappers = mappingLookup.getMapping().getSortedMetadataMappers();
            internalParseDocument(metadataFieldsMappers, context);
            validateEnd(context.parser());
        } catch (XContentParseException e) {
            throw new DocumentParsingException(e.getLocation(), e.getMessage(), e);
        } catch (IOException e) {
            
            throw new DocumentParsingException(XContentLocation.UNKNOWN, "Error parsing document", e);
        }
        assert context.path.pathAsText("").isEmpty() : "found leftover path elements: " + context.path.pathAsText("");
        Mapping dynamicUpdate = createDynamicUpdate(context);
        
        if (dynamicUpdate == null) {
            documentParsingObserver.setIndexName(mappingParserContext.getIndexSettings().getIndex().getName());
            documentParsingObserver.close();
        }
        return new ParsedDocument(
            context.version(),
            context.seqID(),
            context.id(),