Simplify sync2jira onboarding at scale by defining a project link instead of an individual repo

[mattreid]

Today, sync2jira is configured per repository, which can be cumbersome for teams who have many repositories they want to manage. It would be simpler if a team could provide a GH project URL and have sync2jira pull everything that is associated with it. As an example, podman-desktop, has one main repository, and 7 smaller extension repositories. All of these are included into a single project planning board, but to onboard today, they'd need to set up all 8 repositories individually, and adjust their sync2jira configuration each time they added a new repo.

The goal would be to point sync2jira at a GH project board (like this), and have sync2jira use that as the issue list to sync and maintain in Jira, rather than managing a list of repositories individually. Repos added or removed from the project board would then have relevant issues automatically synced (or not) as needed.

One possible additional benefit of this approach could be better support for community repos that we contribute to, but do not own. Setting up the webhooks to export event data requires a high level of buy in from the maintainers of that repository, with little incentive to approve that request. If we could set up a project board that pulls the issues our developers work on each sprint, maybe sync2jira could pull those, without needing access to everything else.