Add the `schema_name` field to the dictionary files

What does this MR do and why?

Add the schema_name field to the dictionary files.

I have used the following script to populate the dictionary files:

gitlab_schemas_path = "/Users/diogo/gitlab-development-kit/gitlab/lib/gitlab/database/gitlab_schemas.yml"
dic_path = "/Users/diogo/gitlab-development-kit/gitlab/db/docs/"
file_names = Dir.entries(dic_path)
gitlab_schemas = YAML.load_file gitlab_schemas_path

file_names.each do |file_name|
  next unless file_name.include? ".yml"

  table_name = file_name.gsub(".yml", "")

  gitlab_schema = gitlab_schemas[table_name]

  file_path = dic_path + file_name
  data = YAML.load_file file_path
  data["gitlab_schema"] = gitlab_schema
  File.open(file_path, 'w') { |f| YAML.dump(data, f) } 
end

More info: gitlab-org/database-team/team-tasks#260 (closed)

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