v0.20.0: Enhanced ephemeral runners and webhook-based autoscaling, New RunnerSet API

CAUTION: If you're using the Helm chart, beware to review changes to CRDs and do manually upgrade CRDs! Helm installs CRDs only on installing a chart. It doesn't automatically upgrade CRDs. Otherwise you end up with troubles like #427, #467, and #468. Please refer to the UPGRADING docs for the latest process.

This is a big release with lots of new features! (sorry if you're off the list, this release included a lot of changes so I've only mentioned the major stuff below, all changes are highly appreciated!)

This release includes the following new features that depends on unreleased new features GitHub is planning to roll out soon:

• Support for new ephemeral runners doc
• New workflow_job-based autoscaling doc

This release includes the following major changes from the following contributors:

• @jstewart612 Don't set default caBundle for webhooks (#617)
• @int128 Add default value of githubWebhookServer.syncPeriod to chart (#622)
• @Puneeth-n doc: Add caveat on volumeMounts (#632)
• @mumoshu doc: Use with Istio (#635)
• @mumoshu doc: Introduce summerwind/actions-runner images (#634)
• @mumoshu @toast-gear feat: RunnerSet backed by StatefulSet (#629)
• @shubhindia We are exiting if its a registration-only runner (#641)
• @sxd Added support to enable and disable enableServiceLinks. (#628)
• @mumoshu Clean up import list (#645)

// TBW