feature: Allow installing extra requirements when using the credentials role

[kewne]

This makes the credentials role support the use of edx_django_service_extra_requirements
as done originally in !6400

The changes here are cherry-picked from the upstream work in https://github.com/edx/configuration/pull/6449

Related links:

• BB-4342 (OpenCraft Internal JIRA)

Testing

1. Launch devstack with credentials service: make dev.up.credentials
2. In the configuration repo, create a docker_inventory.ini file containing just

credentials ansible_connection=docker ansible_host=edx.devstack.credentials

3. Create a playbook credentials_test.yml:

- name: Deploy edX Credentials Service
  hosts: all
  become: True
  gather_facts: True
  vars:
    ENABLE_DATADOG: False
    ENABLE_NEWRELIC: False
    CLUSTER_NAME: 'credentials'
  roles:
    - credentials

4. Run the playbook from the playbooks directory (to ensure ansible.cfg is picked up): ansible-playbook credentials_test.yml -i docker_inventory.ini --skip-tags install:code -e '{ disable_edx_services: true, CREDENTIALS_EXTRA_REQUIREMENTS: [{name: 'lolcat'}], edx_django_service_is_devstack: true}'
5. Assert lolcat is now installed in the credentials virtualenv:

make dev.shell.credentials
source /edx/app/credentials/venvs/credentials/bin/activate
echo test | lolcat 

[lgp171188]

👍

• I did not test this, as it is a straightforward change that is similar to the changes done before for the ecommerce and course-discovery services.
• I read through the code
• I checked for accessibility issues NA
• Includes documentation NA

[pomegranited]

@kewne Could you update this PR description to link to your upstream PR? Helps us during major version updates to track what's "code drift" vs what's been merged upstream.

[kewne]

@pomegranited Done, thanks for the nudge.