…ic#238890)

Fix elastic#223245

Fields of type `flattened` where being mapped as default. This did not
include `ignore_above` field.
This PR fixes the mapping and includes `ignore_above` field if exists.
If the field is not present, it does not use a default value.

Testing done:

- unit test case for `generateMappings` function
- manual testing installing the reported integration and checking the
field is now being mapped.
using `crowdstrike` integration and adding `ignore_above` to the
[flattened
field](https://github.com/elastic/integrations/blob/main/packages/crowdstrike/data_stream/falcon/fields/fields.yml#L689).
once installed, add the integration to an agent policy and verify the
mapping has included the given field

Check the PR satisfies following conditions.

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [ ] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

Fixes `ignore_above` mapping for `flattened` fields

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
(cherry picked from commit aa12bed)