Let 'devctl repo setup' create/update a ruleset 'renovate-automerge'

[marians]

Towards https://github.com/giantswarm/giantswarm/issues/28741, https://github.com/giantswarm/giantswarm/issues/34621

This PR changes the devctl repo setup command so that if the --renovate flag is set true (by default), a ruleset is created to allow Renovate to merge approved PRs.

The ruleset is named renovate-automerge.

If the ruleset with that name already exists in the repo, it is checked for up-to-dateness. If not up-to-date, it is recreated.

This PR also removes the flag --dry-run from the same command, as it had absolutely no function in this command.

Testing

go run main.go repo setup giantswarm/repo-slug

Preview

When the ruleset was not yet in place:

$ go run main.go repo setup giantswarm/renovate-playground
INFO[0000] get repository details for "giantswarm/renovate-playground"
INFO[0000] configure repository settings
INFO[0000] grant permission on repository
INFO[0001] configure protection for "main" branch
INFO[0002] Adding giantswarm/renovate-playground to repositories accessible by Renovate...
INFO[0003] response status: "204 No Content"
INFO[0003] reading ruleset renovate-automerge from repository giantswarm/renovate-playground
INFO[0003] Ruleset for renovate not found in repository giantswarm/renovate-playground, creating it...
INFO[0003] Creating ruleset for renovate in repository giantswarm/renovate-playground
INFO[0003] creating ruleset renovate-automerge in repository giantswarm/renovate-playground
INFO[0003] completed repository setup

When the ruleset existed but was modified:

$ go run main.go repo setup giantswarm/renovate-playground
INFO[0000] get repository details for "giantswarm/renovate-playground"
INFO[0000] configure repository settings
INFO[0000] grant permission on repository
INFO[0001] configure protection for "main" branch
INFO[0002] Adding giantswarm/renovate-playground to repositories accessible by Renovate...
INFO[0003] response status: "204 No Content"
INFO[0003] reading ruleset renovate-automerge from repository giantswarm/renovate-playground
INFO[0003] Ruleset renovate-automerge (ID 9052178) already exists in repository giantswarm/renovate-playground
INFO[0003] Found these differences in ruleset:
  github.RepositoryRuleset{
  	... // 9 identical fields
  	Links:      nil,
  	Conditions: &{RefName: &{Include: {"~DEFAULT_BRANCH"}, Exclude: {}}},
  	Rules: &github.RepositoryRulesetRules{
- 		Creation: nil,
+ 		Creation: &github.EmptyRuleParameters{},
  		Update:   nil,
  		Deletion: nil,
  		... // 18 identical fields
  	},
  	UpdatedAt: nil,
  	CreatedAt: nil,
  }

INFO[0003] Ruleset renovate-automerge (ID 9052178) is not up-to-date in repository giantswarm/renovate-playground
INFO[0003] Deleting ruleset renovate-automerge (ID 9052178) in repository giantswarm/renovate-playground
INFO[0004] Creating ruleset for renovate in repository giantswarm/renovate-playground
INFO[0004] creating ruleset renovate-automerge in repository giantswarm/renovate-playground
INFO[0004] completed repository setup

When the ruleset existed as desired:

$ go run main.go repo setup giantswarm/renovate-playground
INFO[0000] get repository details for "giantswarm/renovate-playground"
INFO[0000] configure repository settings
INFO[0000] grant permission on repository
INFO[0001] configure protection for "main" branch
INFO[0002] Adding giantswarm/renovate-playground to repositories accessible by Renovate...
INFO[0002] response status: "204 No Content"
INFO[0002] reading ruleset renovate-automerge from repository giantswarm/renovate-playground
INFO[0003] Ruleset renovate-automerge (ID 9052072) already exists in repository giantswarm/renovate-playground
INFO[0003] Ruleset renovate-automerge (ID 9052072) is up-to-date in repository giantswarm/renovate-playground
INFO[0003] completed repository setup

Checklist

• Update changelog in CHANGELOG.md.