chore(github): Migrate to renovate GH action

[mkilchhofer]

This is a working WIP to replace Renovate hosted app at (https://developer.mend.io/) with a self-hosted version via the official GitHub action renovatebot/github-action.

PR is to start a discussion whether we want to keep the existing approach introduced by @tico24 here:

• feat(github): Use renovate to create PRs when upstream releases #2358

Status quo

In my point of view it is a bit fragile to synchronize between an App and a GH action. Especially as soon as the GH action adds another commit to update the changelog, Renovate cannot update the PR anymore, otherwise the GH action needs to update the changelog again (unsure whether it works today).

Renovate as a GH action

When we use Renovate as an action, we talk about self-hosted. This ways we are then allowed to execute so-called postUpgradeTasks. Everything then is under full-control of Renovate.

Source: https://docs.renovatebot.com/configuration-options/#postupgradetasks

If we proceed

Things which are open to proceed:

• Create a GitHub App at org level (argoproj) -> reach out to maintainers via Slack
  Grant same permissions as the official App from MEND

  

• Install the app into argo-helm -> Also via Slack
• Add 1 secret to argo helm (GitHub App private key RENOVATE_APP_PRIVATE_KEY)
• Add 1 variable to argo helm (GitHub App ID RENOVATE_APP_ID)

[mbevc1]

Seems reasonable to switch, but also no strong opinions here.

[terrytangyuan]

Things which are open to proceed

Done.

[terrytangyuan]

LGTM