Run gitlab-triage to update old issues/MRs

This is a proposal to automatically update old issues/MRs. I did some tests in this repo: https://gitlab.com/beenje/test-triage/-/tree/test See https://gitlab.com/beenje/test-triage/-/issues/?sort=created_date&state=closed

gitlab-triage is run on schedule only. If an issue or MR hasn't been updated in 1 year, we add the stale label and a comment. After 15 days, if there is still no update, the issue/MR is closed and the stale::closed label is added.

Note that if someone adds a comment in a stale issue/MR, we have to remove the stale label manually. It will still be closed after 15 days without update if the label is present. We can discuss the 1 year/15days period. I took the stale and stale::closed label from https://github.com/conda/conda/issues. Note that we have to create the labels we want to use manually in the project first.

Right now I added the --dry-run flag to the command so we can test without doing any change.

We can also discuss how often to run on schedule. I think nightly would be nice. It will run the tests as well. That shouldn't be a problem now that we have internal runners.

I already added the GITLAB_TRIAGE_API_TOKEN variable to the CI variables.