Add dependabot

[jpchauvel]

Add the following in .github/dependabot.yml:

# To get started with Dependabot version updates, you'll need to specify which
# package ecosystems to update and where the package manifests are located.
# Please see the documentation for all configuration options:
# https://docs.github.com/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file

version: 2
updates:
  - package-ecosystem: "pip"
    directory: "/"
    schedule:
      interval: "weekly"
      day: "saturday"
      time: "16:00"
    ignore:
      - dependency-name: '*'
        update-types: ['version-update:semver-patch']
    labels: ['dependencies']
  - package-ecosystem: "github-actions" # See documentation for possible values
    directory: "/" # Location of package manifests
    schedule:
      interval: "weekly"
      day: "saturday"
      time: "16:00"
    labels: ["dependencies"]