Support overriding batch column for dynamic models

What does this MR do and why?

Related to #408168 (closed)

Gitlab::Database::DynamicModelHelpers provides two methods that wrap each_batch for use in DB migrations and this MR updates both of the two methods.

• Update 1. Support specifying a custom column to batch over.

each_batch supports specifying a custom column like this:

Issue.each_batch(of: 100, column: :created_at) do |batch|
  puts batch.pick("MIN(created_at), MAX(created_at)")
end

However, the wrapper each_batch defined in Gitlab::Database::DynamicModelHelpers did not support specifying a column.

• Update 2. Fix each_batch_range to correctly pick out the primary key of the batch table.

NamespaceSettings's primary key is namespace_id. Using each_batch_range on the table would not yield the correct primary key columns.

• See !118581 (comment 1366429019)
• We actually had a problem in !114423 (comment 1359877440).

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