Add a migration to remove the wiki docs from the main index

What does this MR do and why?

Since wikis are now moved to a separate index, the wiki documents from the main index can be removed.

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Before	After

How to set up and validate locally

Make sure Elasticsearch is enabled

1. Open the Rails console

bundle exec rails c

2. Run the following command

require_relative 'ee/elastic/migrate/20230720010000_delete_wikis_from_original_index.rb' 
DeleteWikisFromOriginalIndex.new(20230720010000).migrate

4. Now check the wiki docs on the main index. It should not have any docs

curl -XGET "http://localhost:9200/gitlab-development/_search" -H "kbn-xsrf: reporting" -H "Content-Type: application/json" -d'
{
  "query": {
    "bool": {
      "filter": [
        {
          "term": {
            "type": "wiki_blobs"
          }
        }
      ]
    }
  }
}' | json_pp

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.

Approximate time to completion

~ 3 hours

[6] pry(main)> number_of_documents = 605_735
=> 605735
[7] pry(main)> batch_size = 10000
=> 1000
[8] pry(main)> throttle_delay = 3.minutes
=> 3 minutes
[9] pry(main)> ((number_of_documents / batch_size) * throttle_delay)/60.minutes
=> 3

Related to #336100 (closed)