This commit does three things:
* Removes all Copyright/license headers for the build.gradle files under x-pack. (implicit Apache license)
* Removes evaluationDependsOn(xpackModule('core')) from build.gradle files under x-pack
* Removes a place holder test in favor of disabling the test task (in the async plugin)
Backport of #59293 to 7.x branch.
* Create new data-stream xpack module.
* Move TimestampFieldMapper to the new module,
this results in storing a composable index template
with data stream definition only to work with default
distribution. This way data streams can only be used
with default distribution, since a data stream can
currently only be created if a matching composable index
template exists with a data stream definition.
* Renamed `_timestamp` meta field mapper
to `_data_stream_timestamp` meta field mapper.
* Add logic to put composable index template api
to fail if `_data_stream_timestamp` meta field mapper
isn't registered. So that a more understandable
error is returned when attempting to store a template
with data stream definition via the oss distribution.
In a follow up the data stream transport and
rest actions can be moved to the xpack data-stream module.
Jake Landis
Martijn van Groningen