Create issue boards for core work

In order to allow each core team to order kanban cards in whatever they see fit, independently from other teams, they need to have their own issue board.

So, for each team that does use its "Core work" label:

• Create an issue board titled "Core work: $TEAM" (just like the label) with the "To Do", "Doing", and "Needs Validation" lists. This issue board must be in the tails/tails project: unfortunately, one cannot create multiple issue boards at the group level.
• Update doc in the corresponding wiki/src/contribute/working_together/roles/*.mdwn page, to link to the corresponding issue board, filtered with the corresponding "Core Work" label

Teams:

• Core work: Foundations Team
• Core work: Technical writing
• Core work: User experience