chore: add dependabot cooldown settings to mitigate ongoing supply chain attacks

[Tethik]

Summary

Adds cooldown configuration to every package ecosystem in .github/dependabot.yml to reduce exposure to ongoing supply chain attacks by limiting how quickly compromised or malicious package versions can be automatically adopted.

cooldown:
  default-days: 7
  semver-major-days: 30
  semver-minor-days: 7
  semver-patch-days: 3
  exclude:
    - github.com/einride/*
    - github.com/einride-autonomous/*
    - github.com/einride-labs/*

Security updates are automatically exempt from this cooldown.