This PR adds an intermediate solution for packaging X-Pack modules with Filebeat. In this PR the dashboards, configuration files, and fields are generated in x-pack/filebeat. Packaging is still done entirely from the OSS filebeat directory by making the build run `mage update` in x-pack/filebeat then customizing the packaging configuration to point to different dashboards, config, and fields.yml for the Elastic licensed packages.

Long term we will build, test, and package the OSS and Elastic licensed Beats from their respective directories, but this gives us a smaller step in order to be able to release the X-Pack content before the build system is fully transitioned.

X-pack and OSS binaries need a different include/assets.go to account
for fields on non-oss modules.

x-pack/filebeat/include/list.go imported suricata module to have it
register its fields, but this is unnecessary in filebeat as it uses one
big fields.go with all modules fields.

It was not properly replacing the beat binary with the x-pack version.

Problems with x-pack fields missing were caused by a mistake in the
packaging templates that caused the oss binary to be used for
darwin/tar.gz package.

In order to fix this issue a few unnecessary changes to the fields.yml
generation were carried out.