Pull pagila DB from github directly

[hhorak]

Discovered as a part of #588, pagila DB is pulled and extracted from an el7 RPM, while it could be pulled from github: https://github.com/devrimgunduz/pagila

[SlouchyButton]

Maybe the reason why RPM was chosen in the first place is to lock it to specific version/have it includes downstream changes (which they were none anyway).

The RPM package is now orphaned (it got orphaned 3 years ago). But to continue with the thought of keeping the SQLs stable just to be safe, we should probably pull them from pagila repo by a specific tag/commit.