[tests-only][full-ci]getting ocis keycloak token using auth code flow

[S-Panta]

Description

This PR adds the code for getting access token for ocis user when keycloak is used as IDP. This is done so that login step can be shifted after all API task is performed. The grant type for getting access token is Authorization Code Grant Type

Related Issue

• Fixes https://github.com/owncloud/web/issues/11307

How Has This Been Tested?

• test environment:
• locally and CI

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Technical debt
• [x] Tests
• [ ] Documentation
• [ ] Maintenance (e.g. dependency updates or tooling)