feat(dependabot): add 7-day dependency cooldown

[thdaraujo]

(Fixes #3262)

Adds a 7-day cooldown for dependency updates on dependabot:

• https://docs.github.com/en/code-security/tutorials/secure-your-dependencies/optimizing-pr-creation-version-updates#setting-up-a-cooldown-period-for-dependency-updates

This could help us mitigate some supply chain attacks.