Adopt Renovate

[marcphilipp]

Motivation

Currently we use a combination of Dependabot, the wrapper-upgrade Gradle plugin, and the Combine PRs GitHub Action in order to keep our build and project dependencies as well as the Gradle version up to date. Instead, we should adopt Renovate which should make dependency updates more manageable.

Deliverables

• Configure Renovate #3950
• Migrate renovate config #3951
• Update all dependencies - autoclosed #3953
• Group PRs by package manager #3955
• Group by package manager regardless of update type #3956
• Delete custom groups #3957
• Check that Gradle version are updated
• Check that dependencies are updated
• Check that GitHub Actions are updated
• Check that auto-merge works
• Delete Combine PRs workflow since it's been replaced with Renovate #3967
• Polish Renovate config #3982
• Set up PR requirement with at least one approval

Identified issues

• Gradle: Support installation of JDK version requested by Gradle Daemon JVM Discovery renovatebot/renovate#30165
• pinGitHubActionDigests not working for `oracle-actions/setup-java@v1` renovatebot/renovate#31342

Open questions

• Can config migration be used for shareable config preset repositories? renovatebot/renovate#31351