add ignore_empty_value parameter in set ingest processor

[gaobinlong]

Relates to #54783.
The main point of this PR is adding ignore_empty_value in set ingest processr, which can exit quitely if the templated value is null or emtpy string when the parameter is set to true.

Because the template value like {{foo}} produces empty string when the field foo does not exist, is null or empty string, so the parameter ignore_empty_value ignores both nullor empty string when it's set to true.

[elasticmachine]

Pinging @elastic/es-core-features (:Core/Features/Ingest)

[danhermann]

@elasticmachine ok to test

[danhermann]

@elasticmachine update branch

[danhermann]

@gaobinlong, this looks great. I left two minor changes below and I'll get it merged if those look good to you.

[danhermann]

@elasticmachine update branch

[danhermann]

@gaobinlong, sorry for the delay on this one. If you can fix the two new compile errors (just add another boolean parameter to the createSetProcessor method in the new tests testSetMetadataIfSeqNo and testSetMetadataIfPrimaryTerm), I will get in merged in promptly so there won't be any more conflicts on it.

[gaobinlong]

@danhermann, I have done that and all checks have passed.

[danhermann]

Thank you, @gaobinlong! I've merged this and will also get it back-ported to the appropriate branches.

[P1llus]

@gaobinlong Just wanted to say thank you for the contribution, I had a issue open on this for a while and it allows me to do some fairly nice changes to pipelines :)