What does this MR do and why?

Describe in detail what your merge request does and why.

Backfills the traversal_ids for blobs and wiki blobs in the main index, more details in the issue #351381 (closed)

Time for completion estimate calculation (internal link): 278 hours (may take a little longer due to having to work through each project). Indexing will not be paused during the migration.

Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Run the following query to get the blobs and wiki_blobs with missing traversal_ids

{
  "size": 0,
  "query": {
    "bool": {
      "must_not": {
        "exists": {
          "field": "traversal_ids"
        }
      },
      "must": {
        "terms": {
          "type": [
            "blob",
            "wiki_blob"
          ]
        }
      }
    }
  },
  "aggs": {
    "my-agg-name": {
      "terms": {
        "size": 1000,
        "field": "project_id"
      }
    }
  }
}

2. Make sure advanced search is enabled and you run the migration from rails console by entering the following lines:

require File.expand_path('ee/elastic/migrate/20221221110300_add_traversal_ids_in_blobs_and_wiki_blobs.rb')
BackfillTraversalIdsToBlobsAndWikiBlobs.new(20221221110300).migrate

3. Run the query again in ES to verify that there are no records with misssing traversal_ids

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #351381 (closed)