Summary:
	Ref T401

	- Fix : The 'ongoing' status wasn't set to the content that were supposed to be
in que archival queue.
	- Refactor :
		- Extract sql query from archive worker and place it into db module
		- Refactor in order to improve code quality & separation and to  simplify unit testing.
		- Change the way the director's configuration is stored to make it easy to send the whole config to ArchiverWorker

Reviewers: #reviewers

Maniphest Tasks: T401

Differential Revision: https://forge.softwareheritage.org/D27