Rename all occurences of "oas" to "stackspin"

.gitlab-ci.yml

.gitlab/ci_scripts/create_vps.sh

.gitlab/issue_templates/bug.md

.gitlab/issue_templates/feedback.md

.gitlab/issue_templates/new_app.md

.gitlab/issue_templates/update_all_components.md

CONTRIBUTING.md

Makefile

README.md

ansible/conftest.py

ansible/conftest.py

ansible/group_vars/all/oas.yml

ansible/inventory.yml.example

ansible/roles/configure/files/README.md

ansible/roles/configure/tasks/main.yml

ansible/roles/configure/templates/version.txt

ansible/roles/pre-configure/tasks/main.yml

ansible/roles/pre-configure/templates/registries.yaml

docs/README.md

docs/customizing.rst