Add stale issue and PR labeler workflows

[thompson-shaun]

This PR adds Close Stale Issues and PR Labeler action workflows. Durations for stale item comments and closure are initial suggestions.

A first attempt was made in a previous PR that had great comments (thanks @crazy-max and @thaJeztah). This iteration drops the 3rd-party auto-labeler and strictly focuses on official GitHub actions.

Goals

• Encourage timely processing of Issues and PRs
• Automatically identify areas being modified by a PR (slight toil reduction, faster binning, may yield insights over time).

Close Stale Issues

Warns and then closes issues and PRs that have had no activity for a specified amount of time.

General

The configuration as proposed will exempt Issues and PRs that have been assigned milestones (even arbitrarily long ones such v-future). In addition, the workflow would process only items created after the start-date. We can adjust this date as desired. There is also an option to exempt items that have been assigned to a user.

exempt-milestones: true
start-date: '2024-05-01T00:00:00+0000'

Issues

Notable configuration options

# durations before stale and close actions are taken
days-before-issue-stale: <integer>
days-before-issue-close: <integer>
# labels applied as the issue transitions from active -> stale -> closed
stale-issue-label: 'stale' 
close-issue-label: 'rotten'
# labels that can be applied to avoid stale processing
exempt-issue-labels: 'frozen'

Pull Requests

Notable configuration options

# durations before stale and close actions are taken
days-before-pr-stale: <integer>
days-before-pr-close: <integer>
# labels applied as the issue transitions from active -> stale -> closed
stale-pr-label: 'stale'
close-pr-label: 'rotten'
# labels that can be applied to avoid stale processing
exempt-pr-labels: 'frozen'

Pull Request Labeler

Automatically label new pull requests based on the paths of files being changed or the branch name.

At present, this is primarily applying area/* labels but can be extended if it helps.