Add query builders for separate SELECT+INSERT copy queries

[danieljoos]

A Pull Request should be associated with an Issue.

We wish to have discussions in Issues. A single issue may be targeted by multiple PRs.
If you're offering a new feature or fixing anything, we'd like to know beforehand in Issues,
and potentially we'll be able to point development in a particular direction.

Related issue (public): #1681
Related issue (internal): https://github.com/github/database-infrastructure/issues/8163

Further notes in https://github.com/github/gh-ost/blob/master/.github/CONTRIBUTING.md
Thank you! We are open to PRs, but please understand if for technical reasons we are unable to accept each and any PR

Description

This PR is part of the move-tables feature development PR stack.
It introduces query builders for separate SELECT + INSERT queries that are used for the move-tables mode instead of the range-INSERT query that usually runs on the primary host.
For move-tables the copy step needs to first SELECT on the source, then INSERT on the target. Of course this comes with much higher cost: copying the data to and from the host that runs gh-ost.

In case this PR introduced Go code changes:

• contributed code is using same conventions as original code
• script/cibuild returns with no formatting errors, build errors or unit test errors.