chore: it's now safe to move renovate config into .github

Turns out renovate wasn't opening PRs only because:
1. issue not enabled in the repo
2. the config file contained an invalid key

Now that these issues are fixed, we can move the config file into
.github to avoid overcrowding the root directory.

renovate.json → .github/renovate.json5

@@ -1,5 +1,4 @@
 {
 	"$schema": "https://docs.renovatebot.com/renovate-schema.json",
 	"extends": ["github>haoqunjiang/renovate-presets:npm.json5"],
-	"forkProcessing": "enabled"
 }