PR and issue automation

[martincostello]

• Add the dependency review action.
• Use the new polly-updater-bot app to apply the .NET SDK updates. This removes the need to close and re-open PRs raised by the workflow to get the CI to run.
• Add a workflow to approve and auto-merge dependabot updates for a trusted set of dependencies.
• Add a workflow to approve and auto-merge .NET SDK updates by the polly-updater-bot app.
• Automatically mark issues and pull requests as stale if there is no activity for 60 days.
• Automatically close stale issues and pull requests after 14 days.

Resolves #1167.

[codecov]

Codecov Report

Merging #1370 (5cf8b26) into main (0f425ec) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1370   +/-   ##
=======================================
  Coverage   83.61%   83.61%           
=======================================
  Files         268      268           
  Lines        6403     6403           
  Branches     1004     1004           
=======================================
  Hits         5354     5354           
  Misses        840      840           
  Partials      209      209           

Flag	Coverage Δ
linux	83.61% <ø> (ø)
macos	83.61% <ø> (ø)
windows	83.61% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[martintmk]

lgtm, but I am no expert in GitHub workflows so take this review with a grain of salt.

[joelhulen]

This looks good to me.

[martincostello]

Cool - thanks both. I'll merge this as-is, and we can tweak anything in a future PR.

[martincostello]

Looks like the updater bot is working: logs

Run peter-murray/workflow-application-token-action@8e1ba3bf161[9](https://github.com/App-vNext/Polly/actions/runs/5424515902/jobs/9863981472#step:3:10)726336414f[10](https://github.com/App-vNext/Polly/actions/runs/5424515902/jobs/9863981472#step:3:11)14e37f17fbadf1db
Found GitHub Application: Polly Updater Bot
Obtaining application installation for repository: App-vNext/Polly
Requesting limitation on GitHub Application permissions to only: {"contents":"write","pull_requests":"write"}
{"token":"***","expires_at":"2023-06-30T16:27:17Z","permissions":{"contents":"write","metadata":"read","pull_requests":"write"},"repository_selection":"selected"}
Successfully generated an access token for application.

[martincostello]

And so does the reviewer 🥳

#1376 (review)

[joelhulen]

Awesome!