Remove GMAv1 Fluentd

Why are we doing this work

GMAv1 has been deprecated and the ability to install GMAv1 ("one-click") applications is due to be removed as part of %14.0, including Fluentd.

Fluentd is an integration owned by ~"group::container security" since it's used to forward Cilium logs to a SIEM of the user's choice.

Once fluendt in GMAv1 is removed, our users need to know how to continue to use their currently installed application.

Documentation: remove fluentd GMAv1 section
Feature flag: only required if done before %14.0
Performance: n/a
Testing: ensure a pre-existing GMAv1 fluentd installation can still be used. Also ensure that the GMAv2 configuration via values.yaml is applied to a pre-existing GMAv1 fluentd installation.

frontend remove Fluentd from the applications tabs in the K8S cluster page (example): app/assets/javascripts/clusters/components/applications.vue, app/assets/javascripts/clusters/constants.js, app/assets/javascripts/clusters/components/fluentd_output_settings.vue, app/assets/javascripts/clusters/services/clusters_service.js, app/assets/javascripts/clusters/stores/clusters_store.js and relates specs,
backend remove app/models/clusters/applications/fluentd.rb and related specs and factories (clusters_applications_fluentd in spec/factories/clusters/applications/helm.rb)
backend remove references to Fluentd in app/services/clusters/applications/base_service.rb, app/views/clusters/clusters/show.html.haml, app/models/clusters/cluster.rb,
documentation remove Fluentd from the documentation for GMAv1 and change all references to new GMAv2