[WIP] Removes "required" field attribute

[pzl]

Change Summary

package spec v3 does not allow for the property required in a mapping definition. This removes our instances of required (which seems to only pertain to @timestamp and ecs.version). Neither of these seem to be manually specified, but may be added as part of our reliance on the ECS build tools. An update to the tooling their may be needed to preserve the removal of this setting? Or a post-build step

This change is branched off of #428, so the changes there may also appear here, until that PR is merged

[elasticmachine]

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• Start Time: 2023-09-29T13:54:44.255+0000

• Duration: 39 min 15 sec

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