clean old environments

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Description

I was testing gitlab ci environments, I've read the documentation(s). I use proper way to create and stop dynamic environment (deployments).
But while I was testing this feature, I created many environments, and now, I can't stop / delete / clean it.
Also it can be just API, to programmatic usage for stopping environments.

Proposal

Give ability to clear old environments, especial it will be useful for environments that was not created with on_stop parameters. And please create documentation.

Links / references

Some screenshots

Overview

What is it? UX proposal.
Why should someone use this feature? If someone have same problem as, he will have troubles with explanation to other developer/QA/client/... where they can look at the production/staging/feature-XXX.
What is the underlying (business) problem?
Problem with demonstration to clients the developed features and progress.
How do you use this feature?

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.

• Feature assurance
• Documentation
• Added to features.yml