Improve CI linter to provide warnings for potential collision of paramaters
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### Problem to solve
In general, more warning/error handling in the CI linter will make it easier for developers to get started with GitLab CI and also make identifying issues in complex/long CI files much easier.
**example usecase:**
When configuring jobs in the gitlab.ci.yml file, some combinations of paramaters can give unexpected results, which can be hard to troubleshoot.
For example:
```
Job:A
script:
- echo 'foo'
Job:B
dependencies:
- Job:A
when: always
```
In this case, Job:B is set to run always, but also has a dependency on Job:A. However, Job:A does not define an artifact, and therefore doesnt run, depsite using the `always` param. This makes it hard to troubleshoot because it
**An additional use case where warnings would be helpful**
Variables are passed to runners securely, but once there - they could be accidentally exposed in the logs.
Detect if the yml file has any jobs that may expose a variable in runner logs - such as `echo $myvar` in the `script:` section. Users are not always aware of this risk, so providing a warning would assist in keeping customers code more secure.
### Target audience
Primaryly DevOps engineers, or, anyone working with CI.
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