Clean backport of #12304
This commit changes the DLQ writer to write to a temporary file
which will be renamed on "completion", to avoid the possibility
of the DLQ reader reading an incomplete DLQ segment. The temp file
will be renamed and made available, either when the capacity of this
segment is reached, or if a configurable 'flush interval' has elapsed
since the last event reached the dead letter queue.
This commit fixes#8022, #10275, #10967
This commit replaces #11127
a 50ms delay helps creating more full batches without practical added latency see #8707
a 64mb page helps PQ perfmance related to a large page size see #8702#8707
* add multi_local source for multi pipelines
* introduce pipelines.yml
* introduce PipelineSettings class
* support reloading of pipeline parameters
* fix pipeline api call for _node/pipelines
* inform user pipelines.yml is ignored if -e or -f is enabled
