Create a doc_id field for data exported from the DocumentDb source

[dlvenable]

Every DocumentDb object must have an _id field. The Data Prepper documentdb source should do two things with this value:

1. Create a metadata field primary_key which is a string representation of that value.
2. Create a new field docdb_id with matches the data from _id. This should use the same mappings as found in DocumentDb simple representations of BSON types #4458.

OpenSearch does not allow sending documents with an _id field. So using the docdb_id will allow saving all the data from a DocumentDb object while also using a valid OpenSearch Id.

Examples

For example, say we have the following DocumentDb documents:

{
  _id: {
    category: "repository", 
    title: "OpenSearch"
  }, 
  url: "https://github.com/opensearch-project/OpenSearch"
}

and

{
  _id: {
    category: "project", 
    title: "opensearch-project"
  }, 
  url: "https://github.com/opensearch-project/"
}

We'd like to retain the original data inside the OpenSearch index.

So the documentdb source should output the following:

{
  docdb_id: {
    category: "repository", 
    title: "OpenSearch"
  }, 
  url: "https://github.com/opensearch-project/OpenSearch"
}
metadata {
  "primary_key" : "{category:"repository",title:"OpenSearch"}"
}

and

{
  docdb_id: {
    category: "project", 
    title: "opensearch-project"
  }, 
  url: "https://github.com/opensearch-project/"
}
metadata {
  "primary_key" : "{category:"project",title:"opensearch-project"}"
}

Say the user has the following sink configuration:

sink:
  - opensearch:
      hosts: ["https://localhost:9200"]
      document_id: "${getMetadata(\"primary_key\")}"
      action: "${getMetadata(\"opensearch_action\")}"

Then, in OpenSearch, this will look like:

{
  _id: "{category:"project",title:"opensearch-project"}"
  docdb_id: {
    category: "project", 
    title: "opensearch-project"
  }, 
  url: "https://github.com/opensearch-project/"
}

Configuration

Also, we should allow users to configure the value used in the source.

documentdb:
  id_key: docdb_id

[dlvenable]

Completed by #4512.