Expedite GDK startup by moving 'make truncate-legacy-tables' to a separate GDK command

Overview

Initially discussed at #1983 (comment 1613101530).

Currently, make truncate-legacy-tables is executed as part of gdk reconfigure command, which runs on fresh installations of GDK. This isn't necessary for new setups, and it's more for transitioning from single database to decomposed database.

The goal of this issue is to move make truncate-legacy-tables out of gdk reconfigure and create a gdk truncate-legacy-tables. This will expedite GDK startup in new installations.

Impacted categories

The following categories relate to this issue:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Steps to replicate (optional)

Proposal (optional)

Environment (optional)

• Operating system name: <!-- output of uname -a command -->
• Architecture: <!-- output of arch command -->
• The contents of your gdk.yml (if any)
• Ruby version: <!-- output of ruby --version command -->
• GDK version: <!-- output of git rev-parse --short HEAD command -->