New dashboard for PRs / github labels

Dear all,

following our discussion last week [1] on PRs and the dashboard, I have

- imported all pending PRs to the RDF-star GH project;
- set up GH actions in all our repos, that add any new PR to the project;
- set up a new view of all pending PRs :

     https://github.com/orgs/w3c/projects/20/views/4


This view is sorted by labels, which is may become messy if PRs get many 
labels, but works pretty well for the moment:

- all issues with the 'need-discussion' label are currently grouped 
together and at the top
- other issues are grouped by the spec:editorial, spec:enhancement and 
spec:substantive labels

----

Regarding the labels, I added a description on some of the labels that 
we inherited from other W3C repos. This is my interpretation of these 
labels (roughly corresponding to class 1, class 2 and class 3 changes as 
per the process [2]), but that's up for discussion:

* spec:substantive: "Issue or proposed change in the spec that changes 
its normative content"

* spec:enhancement: "Issue or proposed change to enhance the spec 
without changing the normative content substantively"

* spec:editorial: "Minor issue or proposed change in the specification 
(markup, typo, informative text)"

Note also that I took the liberty to remove the tag 'Editorial' from a 
bunch of issues / PRs where it was redundant (or used in the place of) 
spec:editorial . As its description says, 'Editorial' is meant for 
errata management.

   best

[1] https://www.w3.org/2023/03/23-rdf-star-minutes.html#t05

[2] https://beta.w3.org/2021/Process-20211102/#correction-classes