chore: set up Renovate for dependency updates [MEC-3447]

[contentful-renovate-rollout]

Sets up Renovate as the dependency-update tool for this repository, part of an org-wide rollout.

Depending on this repo's starting state, this PR does some of the following:

• adds a repo-local renovate.json extending the Contentful shared preset
• for repos that used Dependabot: ports repo-specific behavior (PR limits, ignores, grouping) into local packageRules where still needed, and removes Dependabot-only automation and secret policies
• updates docs that referenced Dependabot

Manual follow-up (not handled by this PR):

• close stale Dependabot PRs and branches once Renovate is active (for repos that used Dependabot)

Migration Confidence: 🟡 Medium

Summary

Migrated from Dependabot to Renovate: added renovate.json extending local>contentful/renovate-config (correct standard preset), deleted .github/dependabot.yml, removed the dependabot vault secret policy from .contentful/vault-secrets.yaml, and updated the CODEOWNERS comment. The migrator also translated the three Dependabot ignore rules into Renovate packageRules (disabling @salesforce/dev-scripts, capping oclif below 3.17.1, and capping clean-stack below 3.0.1) — this was a judgment call not mechanically specified by the migration prompt, and the Dependabot cooldown-days: 15 setting was not carried over (no direct Renovate equivalent, likely intentional via the shared preset).

Files requiring attention

The following files had edge cases or required judgment during migration and should be reviewed carefully:

• renovate.json

[contentful-automation]

🎉 This PR is included in version 2.7.4 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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