Update audit logs docs

[cr7258]

Fix: #5104

1. Update fluent configuration file to account for new log fields.
2. Define <match fluent.**> to capture fluentd logs in top level is deprecated. Use <label @FLUENT_LOG> instead.
3. Remove the kubernetes_metadata plugin filter as it doesn't take effect because <filter kubernetes.**> doesn't match the tag "antrea-networkpolicy" in the source. Additionally, the kubernetes_metadata plugin filter is unable to get the metadata of the container from the antrea audit log due to it is derived from the file name(e.g.,/var/log/containers/fabric8-console-controller-98rqc_default_fabric8-console-container-df14e0d5ae4c07284fa636d739c8fc2e6b52bc344658de7d3f08c36a2e804115.log), the file name /var/log/antrea/networkpolicy/*.log did not provide the container's information.
4. Add a new snapshot of Kibana and update the example of the log in the docs.

[tnqn]

@cr7258 Thanks for the PR.

[qiyueyao]

+1 for <direction>, just one comment on the image.

[antoninbas]

/skip-all