Add migration for backfilling traversal_ids in blobs and wiki blobs

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.

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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)

ee/elastic/migrate/20221221110300_backfill_traversal_ids_to_blobs_and_wiki_blobs.rb

+# frozen_string_literal: true
+
+class BackfillTraversalIdsToBlobsAndWikiBlobs < Elastic::Migration
+  include Elastic::MigrationHelper
+
+  batch_size 100_000
+  ELASTIC_TIMEOUT = '5m'
+  BLOB_AND_WIKI_BLOB = %w[blob wiki_blob].freeze
+  batched!
+  throttle_delay 45.seconds
+  retry_on_failure
+
+  def migrate
+    task_id = migration_state[:task_id]
+
+    if task_id
+      task_status = helper.task_status(task_id: task_id)
+
+      if task_status['failures'].present?
+        set_migration_state(task_id: nil)
+        log_raise "Failed to update projects : #{task_status['failures']}"
+      end
+
+      if task_status['completed'].present?
+        log "Updating traversal_ids in original index is completed for task_id:#{task_id}"
+        set_migration_state(task_id: nil)
+      else
+        log "Updating traversal_ids in original index is still in progress for task_id: #{task_id}"
+      end
+
+      return
+    end
+
+    if completed?
+      log "Migration Completed: There are no projects left to add traversal_ids"
+      return
+    end
+
+    log "Searching for the projects with missing traversal_ids"
+    project_ids = projects_with_missing_traversal_ids
+    log "Found #{project_ids.size} projects with missing traversal_ids"
+    project_ids.each do |project_id|
+      update_by_query(Project.find(project_id))
+    rescue ActiveRecord::RecordNotFound
+      log "Project not found: #{project_ids[0]}"
+    end
+  end
+
+  def completed?
+    helper.refresh_index(index_name: helper.target_name)
+    log "Running the count_items_missing_traversal_ids query"
+    total_remaining = count_items_missing_traversal_ids
+
+    log "Checking to see if migration is completed based on index counts remaining: #{total_remaining}"
+    total_remaining == 0
+  end
+
+  private
+
+  def update_by_query(project)
+    log "Launching update query for project #{project.id}"
+    response = client.update_by_query(
+      index: helper.target_name,
+      body: {
+        query: {
+          bool: {
+            filter: [
+              { term: { project_id: project.id } },
+              { terms: { type: BLOB_AND_WIKI_BLOB } }
+            ]
+          }
+        },
+        script: {
+          lang: "painless",
+          source: "ctx._source.traversal_ids = '#{project.namespace_ancestry}'"
+        }
+      },
+      wait_for_completion: false,
+      timeout: ELASTIC_TIMEOUT,
+      conflicts: 'proceed'
+    )
+
+    if response['failures'].present?
+      set_migration_state(task_id: nil)
+      log_raise "Failed to update project with project_id: #{project.id} - #{response['failures']}"
+    end
+
+    task_id = response['task']
+    log "Adding traversal_ids to original index is started with task_id: #{task_id}"
+
+    set_migration_state(
+      task_id: task_id
+    )
+  rescue StandardError => e
+    set_migration_state(task_id: nil)
+    raise e
+  end
+
+  def count_items_missing_traversal_ids
+    client.count(
+      index: helper.target_name,
+      body: {
+        query: query_missing_traversal_ids
+      }
+    )['count']
+  end
+
+  def projects_with_missing_traversal_ids
+    results = client.search(
+      index: helper.target_name,
+      body: {
+        size: 0,
+        query: query_missing_traversal_ids,
+        aggs: {
+          project_ids: {
+            terms: { size: batch_size, field: "project_id" }
+          }
+        }
+      }
+    )
+    project_ids_hist = results.dig('aggregations', 'project_ids', 'buckets') || []
+    project_ids_hist.pluck("key") # rubocop: disable CodeReuse/ActiveRecord
+  end
+
+  def query_missing_traversal_ids
+    {
+      bool: {
+        must_not: { exists: { field: "traversal_ids" } },
+        must: { terms: { type: BLOB_AND_WIKI_BLOB } }
+      }
+    }
+  end
+end