Add support for if_seq_no and if_primary_term to ingest

[martijnvg]

Currently version and version type are accessible in pipeline:

{
  "set": {
    "field": "_version",
    "value": "{{field1}}"
  },
  "set": {
    "field": "_version_type",
    "value": "{{field2}}"
  }
}

However both are deprecated in a favor of if_seq_no and if_primary_term.
Ingest should support these new method of performing optimistic locking in ingest as well:

{
  "set": {
    "field": "_if_seq_no",
    "value": "{{field1}}"
  },
  "set": {
    "field": "_if_primary_term",
    "value": "{{field2}}"
  }
}

[elasticmachine]

Pinging @elastic/es-core-features

[kiawin]

Hi @martijnvg, would like to give it a try to this issue if that's ok with you :)

[martijnvg]

@kiawin yes, please go ahead and give this a try :)

[mariaral]

Hey @kiawin are you still interested in this issue? If not, I could work on this.

[kiawin]

@mariaral Thank for the interest, please go ahead :)

[mariaral]

@martijnvg I just added a PR regarding this feature. Please have a look.