Multiple use templates
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### Proposal
Allow for templates to be used multiple times.
We have projects that have multi-container built pod setups for deployment.
We need way to have both containers scanned.
Currently the existing template (https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/ci/templates/Jobs/Container-Scanning.gitlab-ci.yml) can only be used once `container_scanning` job. Need a way to use this as a `.container_scanning` that can be extended to be used multiple times:
```
container_scanning-httpd:
needs:
- build httpd
variables:
CS_IMAGE: example.com/user/httpd:tag
extends: .container-scanning
container_scanning-php:
needs:
- build php
variables:
CS_IMAGE: example.com/user/php:tag
extends: .container-scanning
```
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issue