Add rake task to configure Vault

What does this Merge Request do and why?

This MR adds a vault:configure Rake task that configures Vault to allow the fetching from secrets from a specific GDK project. It is used like:

bundle exec rake vault:configure[<project_id>]

It allows secrets to be fetched using the configuration:

test_secrets:
  variables:
    VAULT_AUTH_PATH: gitlab
    VAULT_AUTH_ROLE: gitlab-test-role
    VAULT_SERVER_URL: http://<vault_ip_address>:8200
  secrets:
    TEST_ID_TOKEN:
      id_token:
        aud: '<gdk_address>' # ex. https://gdk.test:3443
    DATABASE_PASSWORD:
      vault: gitlab-test/db/password 
  script:
    - echo $DATABASE_PASSWORD
    - cat $DATABASE_PASSWORD

If gitlab!100281 (closed) has not been merged yet, check out the 356986-aw-add-id-token-keyword branch in gitlab in order to use the id_token feature

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.